











f 3 


NAVAL ORDNANCE 



NAVAL ORDNANCE 


A TEXT-BOOK 

PREPARED FOR THE USE OF THE MIDSHIPMEN OF THE 
UNITED STATES NAVAL ACADEMY . 


BY 

OFFICERS OF THE UNITED STATES NAVY 


ANNAPOLIS, MD. 

THE UNITED STATES NAVAL INSTITUTE 
1921 




Copyright, 1921, by 
J.W. CONROY 
Trustee for U. S. Naval Institute 
Annapolis, Md. 


FEB -2 1321 


£or& Q^affttnore (prtee 

BALTIMORE, MD., U. S. A. 


A60K212 


0 j 


PREFACE 


Recent developments in Ordnance and Gunnery have made it 
necessary to-revise the text-book “ Naval Ordnance,” 1915. 

The object sought in the present revision was twofold. The 
first was to eliminate incorrect or obsolete data and bring the text 
up to date. In this connection it was considered undesirable to 
describe numerous types or marks of guns, mounts, breech 
mechanisms, etc. One modern type was selected in each case and 
every effort made to cover its description clearly and completely. 
The second object sought was to make the book a complete treatise 
on the “ Theory of Ordnance ” in so far as that was possible under 
the limitations imposed. With that end in view the following 
subjects formerly published in separate books or pamphlets have 
been included in the text: 

“ The Elastic Strength of Guns,” 1916, by Philip R. Alger, 
Professor of Mathematics, U. S. N. 

“ Graphic Representation of the Relation of Pressures and 
Shrinkages of Built-up Guns for the States of Action and Rest,” 
by Lieut. Commander L. M. Nulton, U. S. N. 

‘‘Recoil and Recoil Brakes” (new material), by Mr. G. A. 
Chadwick, Chief Draughtsman, Bureau of Ordnance. 

“Practical Interior Ballistics,” a Bureau of Ordnance Pamphlet. 

It was considered undesirable to include a treatise on “ Exterior 
Ballistics ” inasmuch as that subject is so satisfactorily dealt with 
in the present text-book “Ground Work of Practical Naval 
Gunnery.” 

The following officers were asked to contribute chapters to the 
book and grateful acknowledgment is made for the excellent 
material submitted by them : 

Commander H. F. Leary, U. S. N. 

Commander Logan Cresap, U. S. N. 

Commander F. D. Pryor, U. S. N. 

Lieut. Commander F. J. Comerford, U. S. N. 

Lieut. Commander O. M. Hustvedt, U. S. N. 

Lieut. Commander Fitzhugh Green, U. S. N. 

Lieut. Commander M. S. Bennion, U. S. N. 


VI 


Preface 


Acknowledgment is also made of the courtesy and assistance 
of Rear Admiral Ralph Earle, U. S. N., Chief of Bureau of 
Ordnance, and of Commander A. C. Pickens, U. S. N. 

The major portion of the task of editing the various chapters 
and preparing the book for publication was performed by 
Commander F. D. Pryor, U. S. N., assisted by officers of the 
Department of Ordnance and Gunnery. These officers deserve 
great credit for their painstaking work. 

A. P. Fairfield, 

Commander, U. S. Navy. 

U. S. Naval Academy, 

July 20 , 1920. 


CONTENTS 


CHAPTER I. 
Explosive Reactions. 

Explosive Substances. 

Initiation of Explosion. 

Heat of Explosion. 

Velocity of Explosion . 

Pressure of Explosion . 

Temperature of Explosion. 

Gases of Explosion . 

Flame of Explosion . 

Flashless Explosion . 


ARTICLE 


3 

8 

14 

16 

22 

24 

25 

26 


CHAPTER II. 

Service Explosives. 

History of Development of Explosives . 

Explosive Substances—General Characteristics.... 
Explosive Mixtures and Explosive Compounds.... 

Uses of Military Explosives. 

Propellants, Igniters, and Detonating Charges .... 

Manufacture of Smokeless Powder. 

Reworked Powder . 

Smokeless Powder—General Discussion. 

Products of Combustion of Nitrocellulose Powder 

Stability of Nitrocellulose Powder . 

Guncotton . 

Black Powder . 

Trinitrotoluene (TNT) . 

Trinitroxylene (TNX) . 

Picric Acid . 

Tetryl . 

Fulminate of Mercury . 


27 

32 

33 

34 

35 
40 

43 

44 ' 

45 

46 

48 

49 

50 

51 

52 

53 

54 


CHAPTER III. 

Elementary Interior Ballistics. 


Section I. Definition and Scope. 55 

Section II. Fitting the Powder to the Gun. 65 

Section III. Historical Development. 82 

Section IV\ Velocity and Pressure Formulas. 83 

Section V. Application of the Formulas. 100 

Section VI. Further Interior Ballistic Considerations: Energy per 
Pound, Powder; Powder Chamber; Wave Pressures; Temperature 
of Metal in Gun after Repeated Firing; Heat Cracks; Erosion; 

Life of Gun; Droop; and Gun Design. 114 

vii 


































VIII 


Contents 


CHAPTER IV. 
Recoil and Recoil Brakes. 


Development and Application of Hydraulic Brakes. 126 

Principles of the Hydraulic Brake. i 2 7 

Velocity of Free Recoil . I2 ^ 

Velocity of Retarded Recoil . x 3 ° 

Determination of Area of Throttling Orifice. I 3 1 

Work of Resistance . L 3 2 

Hydraulic Brake Force. J 33 

Counter Recoil Force . J 34 

Forces Acting on the Gun During Recoil. J 35 

Pneumatic Counter Recoil System . ^6 

Stresses in Deck Structure Due to Firing. 137 

Trunnion Pressure. T 3 *^ 

Test of Recoil System. *39 


CHAPTER V. 


Naval Rifled Guns. 

General Discussion. 14 2 

Definitions of Parts of Guns, and Kinds of Guns. 1 53 

Designation of Guns and Batteries. if >4 

Rifling. 166 

Conditions Governing Gun Construction. 168 

Basic Law of Gun Construction. 170 

Principles of Gun Construction. 17 1 


CHAPTER VI. 
Elastic Strength of Guns. 


Section T. Introduction, Stress and Strain, Hook's Law, Poisson’jS 

Ratio, Basic Principles, Strains in Simple Solids. 176 

Section II. Stress and Strain in Simple Hollow Cylinders, Derivation 

and Application of Formulas. 191 

Section III. Elastic Strength of Simple Hollow Cylinders, Derivation 
and Application of Formulas, Relations Between Internal and 

External Pressures and Radii Ratios.•... 206 

Section IV. Elastic Strength of Compound Cylinders, Shrinkage, Deri¬ 
vation and Application of Formulas. 217 

Section V. Compound Cylinders Continued, “ Reduced Shrinkage,” 

Derivation and Application of Formulas. 226 

Section VI. Application to Built-up Guns. 237 

Section VII. Elementary Gun Design, Gun Projects. 245 

Section VIII. Gun Computations, The Steps in Computing Radii 

Ratios, Shrinkages, Strengths, etc. 248 

Section IX. Formulas for Compound Cylinders of Four Layers. 254 


CHAPTER VII. 

Graphic Representation of Relation of Pressures and Shrinkages of 
Built-Up Guns for States of Action and Rest. 


Strains and Pressures in Simple Cylinders. 257 

Strains and Pressures in Compound Cylinders. 263 

Diagram for Three Cylinder Assembly. 269 


































Contents 


ix 


CHAPTER VIII. 

Metals Used in Ordnance Construction. article 

Definitions. 273 

General Remarks on Metals .:. 275 

Steel in General—Composition of Steel. 290 

Steel for Ordnance Purposes . 294 

Method of Manufacture of Gun Forgings. 299 

Determination of Physical Properties. 305 

CHAPTER IX. 

Details of Gun Construction. 

Parts. 310 

Shop Work, Inspections and Tests. 311 

Building up the Gun. 320 

Finishing the Gun. 326 

Relining . 341 

Radial Expansion Method of Gun Construction. 343 

Inspections . 355 

CHAPTER X. 

Naval Gun Mounts. 

Nomenclature . 356 

Definitions—Discussion . 359 

Metals Used in Gun Mounts. 369 

General Description of Broadside Mounts. 370 

Action During Recoil. 371 

Frictionless Bearings. 372 

General Discussion of Turret Mounts. 374 

14-Inch 3-Gun Turrets. 383 

The Universal Speed Gear.402 

CHAPTER XI. 

Breech Mechanisms. 

Definitions—Requirements . 427 

Systems of Breech Mechanisms. 431 

Systems of Breech Operation. 444 

Systems of Gas Checks.. 451 

Salvo Latch . 466 

Firing Mechanisms. 467 

Firing Locks. 474 

Semi-Automatic Breech Mechanism . 484 

5-Inch Type—Breech Mechanism.489 

14-Inch Type—Breech Mechanism . 50 1 

CHAPTER XII. 

Naval Gun Sights. 

Preliminary Definitions. 506 

Fundamental Requirements'. 507 

Sight Scales, Ranges and Deflection, Determination of the Graduations 508 

Errors in Range and Deflection . 515 

Arbitrary Scales .. 5 

Multiplying Scales . 522 

Calibration . 5 2 3 









































X 


Contents 


Types of Sights and Sight Mounts. 

Telescope Sights .. 

Parallel Motion Sight Mounts. 

Yoke Sight Mounts . 

Periscopic Sights . 

Bore-Sighting . 

Notes on Care and Handling of Telescopes 
Alignment of Guns and Sights. 


ARTICLE 

... 524 
... 527 
... 53 T 
... 538 
... 539 
... 543 
... 547 
... 552 


CHAPTER XIII. 

Firing Attachments and Gas Expelling Devices. 

Firing Methods ... 

Turret Firing Circuit . 

Broadside Circuit .. 

Firing Keys. 

Care of Attachments .. 

Gas Expelling Apparatus. 


56t 

563 

567 

57 1 

572 
574 


CHAPTER XIV. 


Armor. 

Historical . 580 

Present Manufacture of Cemented Armor. 587 

Non-Cemented Armor . 588 

Inspection and Test . 59 1 

Penetration . 593 

Deck Armor. 606 

Tests and Penetration .••• 611 

Securing Armor . 612 

Light Armor . 616 


CHAPTER XV. 
Projectiles. 


Form—(Length. Nose, After End, Body). 617 

Finish and Weight . 622 

The Bourrelet . 624 

The Rifling—(Kinds, Depth, Twist). 625 

The Rotating Band . 634 

Stability and Flight . 639 

Underwater Attack . 642 

Classification . 643 

Armor Piercers. 644 

Penetration . 651 

Common and Class “ B” (High Capacity) Projectiles. 654 

Special Projectiles (Shrapnel, Illuminating, Smoke and Gas, Target, 

Proof Shot, Markers, Line Carriers). 656 


CHAPTER XVI. 

Ammunition and Ammunition Stowage. 


Definitions. 663 

Ammunition Details . 667 

Assembly of Ammunition . 717 










































Contents 


xi 


ARTICLE 

Marking of Ammunition. 722 

Stowage . 723 

Flooding of Magazines . 729 

Cooling and Ventilation . 736 

Magazine Lighting ... 74T 

Supply . 743 

CHAPTER XVII. 

The Proving Ground. 

General Description .... 746 

Proof of Guns and Mounts. 751 

Proof of Powder . 763 

Proof of Shell . 768 

Proof of Armor . 782 

Froof of Fuses and Tracers. 783 

Proof of Primers . 784 

Proof of Powder Cases. 788 

Proof of High Explosives . 789 

Experimental Work. 790 

Measurement of Velocities and Pressures; Instruments and Methods. . 792 

CHAPTER XVIII. 

Aircraft, Anti-Aircraft, and Field Guns. 

Aircraft Guns . 809 

Anti-Aircraft Guns . 817 

Machine Guns (Browning Type) . 822 

3-Inch Landing Guns. 828 

























CHAPTER I. 

EXPLOSIVE REACTIONS. 

Section I.—Explosive Substances. 

1. An explosive substance may be defined as a chemical system 
which is capable, when subjected to a suitable initial impulse, of 
nearly instantaneous chemical decomposition or transformation, 
with evolution of heat and formation of decomposition products 
some of which are gaseous. An explosive reaction is always 
accompanied by a sudden rise of pressure due to the formation 
of gases and to their expansion by the heat liberated in the 
reaction. 

2 . Among explosive substances are included a wide range of 
mixtures and of homogeneous chemical compounds. In general 
the explosive reactions to which they give rise are characterized 
either by (a) an extremely rapid combustion, or by (b) a re¬ 
arrangement of molecules which proceeds practically instan¬ 
taneously. 

In the explosives giving rise to reactions of the first of the above 
classes, oxygen is always present, with one or more combustible 
elements. The oxygen is supplied in such form as to permit the 
oxidation or combustion to proceed without support from outside 
sources. The reaction in these explosives is a true burning which 
proceeds from point to point throughout the explosive, acceler¬ 
ated by the heat and pressure produced. These explosives are 
therefore known as burning explosives, or as progressive or low 
explosives. Among the well-known explosives of this kind are 
black powder and the smokeless powders of various classes. 

In those explosives giving rise to reactions of the second of the 
above classes, oxygen is nearly always present with combustible 
elements such as carbon and hydrogen, being usually held in the 
system in weak bonding radicals, most frequently in the NO, or 
nitro group. In these explosives the chemical arrangement is one 
of unstable equilibrium and the initial impulse brings about a 
breaking down of chemical bonds and a rearrangement of mole¬ 
cules which is so rapid that the evolution of heated gaseous 


2 


Naval Ordnance 


products is practically simultaneous throughout the mass. Such 
explosives are known as detonating or high explosives. That 
the presence of oxygen is not an essential to the formation of 
detonating explosives is demonstrated by the existence of certain 
detonating explosives such as the metallic azides, or metallic salts 
of hydronitric acid, e. g., lead azide, PbN 0 , which contain no 
oxygen. Explosives of this kind are usually in such unstable 
chemical equilibrium that a slight impulse serves to bring about 
the rearrangement of molecules and evolution of heated gas. 

It should be noted that the physical state of an explosive has an 
important influence upon the character of the reaction, and may 
determine whether the explosive is to be assigned to one or the 
other of the classes above mentioned. Thus, certain cellulose 
nitrates in the form of guncotton can be detonated by the applica¬ 
tion of suitable shock, whereas cellulose nitrates capable of being 
formed into solid colloid solution are the principal components of 
the various modern smokeless powders, which are progressively 
burning explosives. The manner in which the decomposition of 
an explosive is initiated and the condition under which it pro¬ 
gresses also influence the character of the reaction. Many of the 
detonating explosives can, by the application of flame, be burned 
in the open with a very moderate rate of combustion and are 
detonated in the same physical state only by the application of a 
very powerful shock. The slow burning of these substances can, 
however, hardly be called an explosive reaction. 

Section II.—Initiation of Explosion. 

3 . I he initiation of an explosive reaction is brought about by 
the application of energy in some form—usually by heat, impact, 
or friction. Many explosive substances can be exploded by the 
use of any one of the above-named forms of energy applied in 
the proper degree and manner. The amount of energy necessary 
to initiate explosion is a measure of the sensitiveness of the ex¬ 
plosive to that particular form of application of energy. The 
total energy necessary may be quite different for the different 
forms of initiating impulse, bor each explosive there is usually 
one preferred or common form of initiation. In technical and 
military usage heat and impact, in some form, are the most 
common. 


Explosive Reactions 


o 

4. Initiation by heat. — l'he burning explosives are commonly 
ignited by the application of heat, more particularly by flame. 
Most of the detonating explosives are capable of explosive de¬ 
composition by heat, especially if heat is applied suddenly in 
sufficient amount throughout the mass. They are also gradually 
decomposed by even moderate heat and this decomposition be¬ 
comes accelerated by the heat liberated in the decomposition, and 
finally an explosion proper may result. This latter action, with 
most of the commonly used explosives, would require a very long 
period for its development. 

5. Initiation by impact. —It is generally considered that in 
initiation by direct impact the action is due principally to the 
conversion of the energy of impact into heat, through pressure 
and friction. This method is found in common use in the various 
forms of percussion firing mechanisms in use in small arms and 
in larger ordnance, in torpedoes and in various forms of mines. 
In these devices it is only in the cap or primer, the first member 
of the explosive train, that the reaction is brought about directly 
by impact. An explosive substance sensitive to shock and friction 
as well as direct heat, usually some mixture containing fulminate 
of mercury, is used in a thin-walled cap which receives the impact 
of the firing pin. The flame and heat from the cap may be used 
to propagate further ignition through various courses to the main 
explosive charge or to initiate detonation through an intermediate 
chain, the first member of which is capable of detonation through 
heat alone. 

6. Detonators. —Most detonating explosives, such as are used 
for the main charge in torpedoes, mines, and high-explosive shell, 
as well as in many forms of blasting, require for initiating their 
action a sudden application of very strong shock, such as is given 
by the detonation of another charge in contact with or in close 
proximity to them. This impulse is usually supplied by a sensitive 
detonating substance, such as fulminate of mercury and its 
mixtures, which can be detonated readily by the application of 
heat. 

The devices used to initiate detonation in larger charges are 
called " detonators They consist usually of a charge of ful¬ 
minate of mercury, or its equivalent, which is detonated by flame 
from a percussion cap, as described above, or, in electric deto- 


4 


Naval Ordnance 


nators, by flame from explosive substances ignited by contact 
with a bridge wire which is heated to incandescence by the firing 
current. In many forms of detonating charge there is an inter¬ 
mediate charge, or booster, between the detonator and the main 
charge. The booster charge contains more explosive than the 
detonator, but is small as compared with the main charge. As 
its name indicates, the booster charge is designed to multiply the 
impulse given by the detonator, providing a shock of sufficient 
intensity to propagate the reaction in all directions to the main 
charge. The explosive substance of the booster charge must 
obviously, either in constitution or in form, be more sensitive to the 
impulse of the detonator than is the substance of the main charge. 

The initiation of explosion by “ detonator ” may be considered 
to partake of certain of the characteristics of initiation by heat 
and initiation by impact, since both heat and impact forces are 
provided by the detonator. That it is not limited by these ele¬ 
ments alone may be shown by the fact that explosions can be 
initiated by influence without the direct application of heat or of 
impact, as generally understood. 

7 . Initiation by influence.—It has been frequently demon¬ 
strated that detonation in an explosive mass can be transmitted 
to other masses of detonating explosives in the near vicinity, with¬ 
out actual contact. It has been generally accepted that such trans¬ 
mission is due to the passage of an explosive percussion wave 
from one mass to the other. The influence of this explosive wave 
upon the second mass is such as to reproduce in it the detonating- 
transformation. 1 he second explosion occurring under these con¬ 
ditions is said to be initiated by influence. The secondary explo¬ 
sion or detonation is also frequently called a sympathetic explo¬ 
sion or detonation. The distance through which this action takes 
place varies with the kinds of explosive involved, the intervening 
medium and other conditions. Explosive waves will be discussed 
more fully in following paragraphs. 

Section III. —Heat of Explosion. 

8 . An explosive reaction is always an exothermal reaction; that 
is, it is accompanied by a liberation of heat. The amount of heat 
or number of heat units set free may be found by applying known 
thermochemical laws. 1 he applicability of these laws to explosive 


Explosive Reactions 


5 


reactions has been found and demonstrated by various investi¬ 
gators, particularly by Berthelot. 

9. Heat of formation. —The application of these laws depends 
upon knowledge of the heats of formation of the initial substances 
and of the products of explosion. 

The “ heat of formation ” of a chemical compound is the 
amount of heat given off or taken up when the compound is 
formed from its constituent elements. 

Heats of formation have been determined for most chemical 
compounds, and are usually expressed in terms of large calories 
per molugram, the molugram of a substance being as many grams 
as there are units in the molecular weight of the substance (thus 
for HoO the molecular weight is 18, and the molugram of H .,0 
is 18 grams). The small calorie is the quantity of heat required 
to raise the temperature of i gram of water (i cubic centimeter) 
from o° C. to i° C. The large calorie is 1000 small calories. 
The simple elements such as oxygen and nitrogen, those names 
being found often in the products of explosives, have no heats of 
formation. 

10. Calculation of heat of explosion. —The thermochemical 
principle on which the calculation of heats of explosives is based 
has been expressed as follows: The heat liberated by a change of 
chemical condition in a system is equal to the excess of the heats 
of formation of the final products over the heat of formation of 
the initial substance. This relation holds whether the final prod¬ 
ucts are all gases or are gases and solids. It is also independent 
of the intermediate transformations which may take place before 
the final state of equilibrium is reached. 

If we denote by Q the heat of the explosion, by Q x the heat of 
formation of the explosive substance, and by Q 2 the sum of the 
heats of formation of the final products of the explosion, the rela¬ 
tion expressed above becomes 

Q=Qo~Qi- 

If the heat of formation of the explosive substance is negative 
(that is, if it is an endothermic body, one whose formation is 
accompanied by absorption of heat) the above equation becomes 

q=q 2 +q 1 . 

In many explosives the final reaction products may differ some¬ 
what, depending upon the conditions under which the explosion 


6 


Naval Ordnance 


takes place, and determination of the exact amount of heat liber¬ 
ated in any given explosion of such a substance will depend upon 
a knowledge of the exact constitution of the final products. The 
final products being known, the heat of explosion, referred to 
constant pressure and to a temperature of 15° C. for both the 
initial substance and the final products, may be calculated as in 
the following example: 

The explosive decomposition of picric acid may be written as 
follows: 

Molecular weights ..229 44 18 28 2 28 

2C 6 H 2 (NO,).,OH = CO, + H 2 0 +11 CO + 2H, + 3N, 
Heats of formation. .46.8 94.3 58.3 26.1 o o 

The sum of the heats of formation of the final products is 
94.3 + 58.3+11x26.1=429.7. The heat of formation of the two 
molugrams of the initial substance which appear in the above 
reaction is 2x46.8 = 93.6 

Q = Q 2 ~Qi = 429-7 - 93-6 = 336 .1 • 

The heat liberated by the explosive decomposition of one molu- 
gram of picric acid is, since two molugrams are represented in 
the above calculation, 168.05 large calories. 

Since the molugram of picric acid is 229 grams, the heat 
liberated by the explosive decomposition of 1 kilogram of picric 

acid is 1 X 1000 = 755.9 large calories. 

' 229 

11. When the heat of explosion is referred to constant pressure, 
as in the above example, the explosive reaction taking place for 
instance in the open air, there is a heat loss equivalent to the work 
performed in expanding the gases and compressing the surround¬ 
ing atmosphere. When the explosive and its decomposition 
products are confined to a constant volume throughout the reac¬ 
tion, the heat developed is increased by the addition of this heat 
equivalent. The relation between the heat developed at constant 
volume, Qtv, and that developed at constant pressure, Qt p , is as 
follows: 

Q tv= Q tp + 0 .$ 4 (n 1 — n) +0.00 2 (n 1 -n)t, 

in which n and n 1 are, respectively, the number of units of volume 
shown in the chemical equation before the reaction and after the 
reaction, and t is the temperature of the surrounding atmosphere 



Explosive Reactions 


7 


In solid and liquid explosives the original volume is so small as 
compared with that of the gases evolved that n may be neglected, 
and we may write 

Qtv=Qtp + -f- 0.002)?! t. 

12. Measurement of heat of explosion.—Practical measure¬ 
ments of heats of explosion are carried out with very small 
amounts of explosive substances, fired electrically in a bomb 
calorimeter, which is similar in principle to the water calorimeter 
used in ordinary determinations of fuel values, but more strongly 
made. The water surrounding the bomb is constantly stirred 
after the explosion, and its rise in temperature is observed by 
means of a thermometer. The increase in temperature multi¬ 
plied by the known water equivalent of the calorimeter gives the 
heat of explosion. 

13 . Heat energy of the reaction.—The heat of explosion rep¬ 
resents the energy of the explosive system and hence its potenti¬ 
ality for work. This, however, does not give a real index of the 
capability or suitability of an explosive substance for a given 
purpose. The velocity at which the reaction takes place, the 
means necessary to initiate it, and a number of other character¬ 
istics to be discussed later, must be considered in selecting an 
explosive for a given purpose. 

The energy content of explosives is much smaller than that of 
the commonly used fuel substances. For example, one kilogram 
of coal gives about 4000 calories, whereas the cellulose nitrate 
smokeless powders used in our guns give about 900 calories per 
kilogram. The velocity with which explosive substances liberate 
their heat is the chief characteristic which makes them valuable 
for the uses to which they are put. 

Section IV.—Velocity of Explosion. 

14 . The velocity of explosive reaction may vary within rather 
wide limits, depending principally upon the kind of explosive 
substance under consideration and upon its physical state. Refer¬ 
ence has already been made to the broad classes of burning 
explosives and detonating explosives and to the fact that certain 
explosive substances, such as cellulose nitrates, may, by changes 
of form and by additions, be used in either class. This behavior 


8 


Naval Ordnance 


of cellulose nitrates indicates the possible effect of physical state 
upon the velocity of reaction in an explosive. 

The velocity of explosive reaction is much greater in the deto¬ 
nating or high explosives than in the burning explosives. The 
rate at which combustion proceeds in cellulose nitrate powders, 
for instance, in modern guns, is of the order of 12 cm. per 
second; whereas the velocity of detonation of high explosives 
ranges from about 2000 to 8000 meters per second. 

It is generally considered that the velocity with which the 
initiating impulse is delivered may influence materially the velocity 
with which explosion is subsequently propagated, especially in 
high explosives, but this subject has not been investigated fully. 
For most practical purposes it may be considered that velocity of 
reaction in a given explosive substance in a given physical state 
is modified principally by its temperature and by the pressure 
under which the reaction takes place. Both of these elements, 
as they increase in value, accelerate the explosive reaction. The 
accelerating influence of increased pressures, especially in the 
burning explosives, is marked. Smokeless powders, containing 
nitrocellulose, or nitrocellulose with nitroglycerin, burn in the 
open or at atmospheric pressure at very moderate velocities; 
when burned in a confined space, as in a gun chamber, they are 
subjected to greatly increased temperature and pressure and their 
combustion is accelerated rapidly, the mean velocity of combus¬ 
tion under these conditions becoming roughly one hundred 
times greater. These increases in velocity of combustion are 
due principally to increased pressure. The smokeless powders, 
being homogeneous solids formed into grains of considerable 
thickness, burn in parallel or concentric layers, the combus¬ 
tion proceeding from one layer to the next throughout the 
mass. The increase of pressure as combustion proceeds brings 
the resultant heated gases in closer contact with each succeeding 
layer and the accelerated combustion results. Black powders are 
mixtures of materials not homogeneous; their grains are less 
uniform and more subject to crushing, and their structure is such 
as to give fine interstices within the grain for the passage of 
heated gases. Hence they do not burn as progressively from 
layer to layer as the smokeless powders do, and their rate of com¬ 
bustion is not so much influenced by increases of pressure. 


Explosive Reactions 


9 


15 . Wave of detonation.— J he velocity with which the ex¬ 
plosive reaction occurs in detonating explosives has already been 
referred to. ihe transformation occurring in these explosives is 
propagated from point to point throughout the mass of the ex¬ 
plosive by a progressive impulse due to the chemical reaction 
occurring. In this transformation there is a constant conversion 
of chemical energy into heat and mechanical energy, and the 
breaking down of chemical bonds is thus sustained throughout 
the mass of the explosive. This transformation is generally 
known as the “ zvave of detonation.” As previously stated, its 
velocity is very great, reaching more than 8000 meters per second 
in some explosives. The analogy between the detonation wave 
and other wave phenomena, such as sound waves, has been pointed 
out by some investigators. The detonation wave, like the sound 
wave, is transmitted at uniform velocity through a homogeneous 
medium and is subject to similar retardation in passing through 
restricted passages. It will be noted, however, that the velocity 
of the detonation wave is much greater than that of the sound 
wave in the same medium. There are other differences, some of 
which are complex and only imperfectly known. Expression by 
formulas of the relation between velocity of detonation and the 
other characteristics of various high explosives has been attempted 
with only partial success. 

In a detonating reaction the force exerted expresses itself in 
two different forms. The first is the detonation wave already 
described, the effect of which is transmitted as a percussion blow, 
similar to the blow of a “ water hammer,” throughout the sur¬ 
rounding media. This has often been called a “ static ” blow. 
The second is the purely physical application of force due to the 
expansion of the gases resulting from the reaction. The action 
of this “ wave ” or force decreases in intensity with the square of 
the distance and it exercises its principal effect in the rending or 
crushing action of the rapidly expanding gases themselves or in 
the similar action of the surrounding material or medium actually 
propelled by their expansion. 

The difference between the two effects discussed above is 
especially marked in underwater detonations. The percussive 
“ hammer blow ” due to the effect of the detonation wave is felt 
and recorded first in all directions from the detonation, sometimes 


io 


Naval Ordnance 


at considerable distances. The second manifests itself in the 
upheaval of masses of water propelled by the escaping gases. 
When the detonation occurs in contact with or near a vessel or 
other solid object, this second effect is added to that of the per¬ 
cussive wave in producing structural damage, and is the principal 
destructive factor. This applies particularly to surface vessels, 
or floating objects which are within the zone of the action. Sub¬ 
merged objects, such as submarines, even though not within the 
destructive range of the second effect here described, are sub¬ 
jected to an encircling pressure from the percussive wave and are 
therefore liable to damage from this cause. I his crushing 
pressure may be sufficiently serious at moderate distances to sink 
or disable a submarine. It is this effect which makes a well- 
placed depth charge so effective against a submarine, even though 
the vessel may be outside the zone of the propulsive action of the 
expanding gases. 

Section V.—Pressure of Explosion. 

16 . We have seen that the high pressure accompanying ex¬ 
plosive reaction is due to the formation of gases which are 
expanded by the heat liberated in the reaction. The work which 
the reaction is capable of performing will depend, disregarding 
heat losses, upon the volume of the gases and amount of the heat 
liberated. The maximum pressure developed and the way in 
which the energy of explosion is applied will depend further upon 
the velocity of the reaction. 

When the reaction proceeds at a comparatively low velocity the 
gases receive heat while being evolved at a moderate rate and 
the maximum pressure is attained comparatively late in the 
reaction. 

If in the explosion of another substance the same volume of 
gas is produced and the same amount of heat is liberated, but the 
velocity of reaction is greater, the maximum pressure will be 
reached sooner and will be greater than in the preceding case. 
Disregarding heat losses, the work done will, however, be equal. 
Heat losses occur principally through the transmission of heat to 
the surrounding medium through conduction and radiation. 
When the time of the reaction is less because of its greater 
velocity these losses are reduced and the heat applied to the per- 


Explosive Reactions 


i r 


formance of useful work through expansion of the gases is 
greater. 

If the evolution of the gases could take place instantaneously, 
the maximum pressure would also be reached at once and the heat 
losses would be reduced to a minimum. 

But for the heat losses, the expansion of the gases after the 
explosive reaction itself is complete could be considered a true 
adiabatic expansion. 

17 . The rapidity with which an explosive develops its maximum 
pressure is the principal factor of the explosive quality termed 
brisance. A “ brisant explosive,” generally so-called, is one in 
which the maximum pressure is attained so rapidly that the effect 
is to shatter material surrounding it or in contact with it. 

18 . In the following brief discussion of the properties and 
action of the gases resulting from explosive reactions, let 

?/ 0 = the specific volume of the gas, that is, the volume of 
unit weight of the gas at a temperature of o° C. and at normal 
atmospheric pressure. 

/> 0 = the normal atmospheric pressure, 103.33 kilograms per 
square centimeter. 

j; ot = the volume of unit weight of the gas at t° C. and 
normal atmospheric pressure. 

/> = any pressure to which the gas may be subjected. 

t; = the actual volume of unit weight of gas at pressure p 
and temperature t° C. 

a = the co-volume of the gas, which is the .least volume into 
which unit weight of the gas can be compressed. In this 
volume the molecules of the gas are regarded as in actual 
contact with each other. (See Art. 20.) 

W — the work done by the gases in expanding. 

A = the density of loading, that is, the ratio of the weight 
of the explosive to the weight of a volume of water which 
would fill the chamber in which the explosive is contained. 

c— the specific heat of the gas, that is, the quantity of heat 
required to raise the temperature of unit weight of the gas 1°. 

T=the absolute temperature of the Centigrade scale. 

19 . Laws of perfect gases.—The following laws have been 
enunciated to express the properties of theoretically perfect gases. 
Actual gases do not follow these laws exactly, especially with 
changes of temperature and pressure. 


12 


Naval Ordnance 


Avogadro’s law.—Equal volumes of gases at the same tem¬ 
perature and pressure contain the same number of molecules. 
Otherwise expressed, at the same temperature and pressure the 
densities of gases are proportional to their molecular weights. 
The molecular volumes of all gases, each being the volume of one 
molugram of the gas at o° C. and at normal atmospheric pressure, 
are therefore equal. 

Mariotte’s law.—At constant temperature the pressure of a 
given weight of gas varies inversely as its volume, or, at t° C., 

pv = p 0 v ot = a constant. 

Gay-Lussac’s law.—At constant pressure the coefficient of 
expansion of a gas for a rise in temperature of i° is a constant, 
for all temperatures and pressures. The value of this constant for 
a rise in temperature of i° C. is 1/273. From this law 



From the above equations we may derive by combination the 
characteristic equation of perfect gases, 


pv = p 0 v 0 1 + 


273 

Since is a constant quantity for a given gas this is written 

pv = R(273 + i). 

273 + t is the absolute temperature in the Centigrade scale, or T. 
Hence 

pv — RT. 


20. To express a similar relation for actual gases, in which the 
observed differences in their behavior from the theoretical be¬ 
havior of perfect gases are taken into account, Clausius proposed 
the following form of a formula of Van der Waal: 


p(v — a ) =RT — 


C ("V — a) 
T(v + / 3) 2 * 


The correction a is known as the co-volume and may be roughly 
explained as follows: A “ perfect ” gas should be infinitely ex- 



Explosive Reactions 


13 


pansible or compressible. To be infinitely compressible its mole¬ 
cules must be compressible, but our conception of a gas is of a 
number of incompressible molecules not cohesive, but separated 
by varying distances dependent upon the rarefaction of the gas. 
The volumes of the molecules themselves are summarized into the 
fraction a of the total volume of the gas, and this fraction a is 
then termed the co-volume. The remaining volume or V— a is 
considered the true volume of the gas for purposes of analysis, 
following the equation above.* 

For gases at o° C. and atmospheric pressure where V represents 
the volume of the gas, u is taken as .001. For smokeless powder, 
however, where V represents the solid volume of the powder, 
subsequently to be converted into gases, the amount of the gases, 
when liberated in the volume occupied by the solid powder, is so 
great that the correction a, in that volume, is approximately f. 
Dififerent investigators assign values from .57 (as for black 
powder also) to 1.1 (a German authority). The mean value of 
it, or the reciprocal of the density of the powder, is employed in 
United States practice. 

The constant /3 is based upon the cohesion of the gases. The 
constant C decreases very rapidly with increase of T, so that at 
the high temperatures attained in explosive reactions the second 
member of the equation approaches zero and may be disregarded. 
Hence, for explosive reactions, we may write the equation 

p (v — a) —RT. 

This equation, which agrees closely with the observed behavior 
of actual gases, may be called the characteristic equation of actual 
gases. It expresses the maximum pressure which the products of 

* One molecule of fulminate of mercury undergoes explosive decomposi¬ 
tion according to the equation, 

Hg(CNO)* = 2CO + N, + Hg. 

if these four molecules of gas should be compressed, their volume 
would decrease in proportion as the pressure increases, but only to a certain 
point where the molecules actually come in contact with each other. This 
volume, although it is greater than the volume of the molecule of mercury 
fulminate, cannot be further decreased. It represents the lower limiting 
volume of the new-formed molecules and is called the co-volume of the 
mercury fulminate. 


14 


Naval Ordnance 


explosion of the unit weight of an explosive exert upon unit 
surface in volume v. 

For any weight To of gas occupying volume V, the maximum 
rj RTo ) 

pressure F — -- . 

By definition (Art. 18), A = ~ or V= N , which value of V, 

substituted in the equation, gives the relation between maximum 
pressure and density of loading, A, as expressed by the equation 

p=^±. 

I — aA 

21 . Expansion of gases.—Mention has already been made of 
the fact that the heat imparted to the resultant gases of the ex¬ 
plosive reaction furnishes the energy which the expansion of the 
gases converts into work. As the gases expand they give up their 
heat, just as steam does in expanding in an engine, and their 
temperature falls. The work done, whether it is expressed in 
propelling or disruptive force, or given up in heat to surrounding 
media, depends upon the number of heat units liberated by the 
explosive into its gases. The work which can be performed by 
one large calorie, the unit used in the preceding discussion of the 
heat of explosion, is 425 kilogram meters. This is the mechanical 
or work equivalent of heat, usually denoted by E. In determining 
the work of which an expanding gas is capable, the specific heat 
of the gas must be known. The specific heat of a given gas may 
vary with the temperature and is ordinarily determined under (a) 
constant pressure, (b) constant volume. If c p is the specific heat 
of the gas at constant pressure, and c v its specific heat at constant 
volume, the work of which unit weight of the gas is capable for a 
change of i° in temperature is W — ( c p — c„)E. 

Since the conditions for adiabatic expansion require that no 
heat be added to or given up by the gas in expansion, the expan¬ 
sion of the gases of explosion can be considered to follow adiabatic 
laws only in part. In a burning explosive heat is being added 
practically throughout the useful expansion because of the com¬ 
paratively moderate progress of the reaction. Furthermore, under 
these conditions a considerable quantity of heat is given off during 
the expansion in heating surrounding materials, such as the gun 
barrel, for instance, in the case of propellent powders. The gases 




i5 


Explosive Reactions. 

from detonating reactions follow more closely the adiabatic laws, 
since the entire volume of gas is evolved almost instantaneously 
and, under usual conditions, the expansion and performance of 
work proceeds with great rapidity with a minimum loss of heat. 

Section VI.—Temperature of Explosion. 

22 . If all of the heat liberated in an explosive reaction were 
applied to the heating of the products of explosion, the rise of 
temperature in these would be 

j. - Q mv 
mv 

Qmv being the heat of explosion for constant volume, and c mv the 
mean specific heat of the products of explosion. 

Experimental determination of the specific heats of gases and 
other substances at the extremely high temperatures involved in 
explosive reactions is difficult. Various investigators have en¬ 
deavored to find the true or relative values involved. It is usually 
assumed that the specific heat varies with the temperature in 
accordance with the equation 

c mv = a + bt, 

in which a and b are constants determined experimentally. 
Substituting this value in the foregoing equation, we get 

Qmv = Qt + bt 2 

and 

l _ — fl +Vfl" +4^ ‘ Qmv 

1 -i*- 

Mallard and Le Chatelier in their comprehensive investigations 
of this subject deduced the following values of a and b for certain 
of the commonly occurring gaseous products of explosion, c mv 
being expressed in small calories: 

C 0 2 ‘, S 0 2 .0 = 6.26, b = 0.0037 

H ,0 (vapor) .0 = 5.61, b = 0.0033 

N.,, Ho, Oo, CO..a = 2.80, b = 0.0006 

If, as in the earlier discussion of heat of explosion, O mv is 
expressed in large calories, its value in the last equation must be 
multiplied by 1000 in using the values given for a and b and hence 
for c mv . If the products of explosion are partly solid the quantity 








i6 


• Naval Ordnance 


of heat absorbed in raising their temperature must be taken into 
account. By way of example, and to illustrate the extremely high 
temperatures attained, it may be mentioned that the calculation of 
the explosive temperature of nitroglycerine by the above method 
has resulted in 3470° C. 

23 . The value of the maximum temperature of explosion is of 
practical technical importance in certain applications of explosives. 
In gaseous coal mines, for instance, the temperature at which the 
gases present are capable of being ignited would influence the 
choice, of the blasting explosives used in the mines. Generally, 
however, the permissible explosives are determined by direct 
experimental means. In guns the temperature of explosion or 
combustion attained influences tbe accuracy-life of the guns by its 
effect upon the erosion. 

Since the practical measurement of explosion temperatures is 
nearly impossible with present means, their theoretical calculation 
is of value, especially as the actual temperatures attained may be 
assumed to be less than the calculated maxima. 

Section VII.—Gases of Explosion. 

24 . In the foregoing discussion of explosive phenomena it has 
been implied that the products resulting from explosive reactions 
are capable of quantitative determination, and that the chemical 
changes occurring throughout the reactions are known. Prac¬ 
tically such information can usually be gained only approximately. 
The usual method involves the explosion of small quantities of the 
explosive substance in a strong container or bomb from which the 
air has been evacuated. When the pressure within the bomb has 
attained a standard condition by cooling, the gaseous products 
are drawn off for examination and the solid products removed by 
washing out. During the interval between explosion and exami¬ 
nation, the conditions surrounding the products of explosion have 
thus undergone changes which may have resulted in alteration in 
their constitution. Their composition at the moment of explosion 
must therefore be estimated by theoretical considerations, aided 
by knowledge of the compositions of the initial substance and of 
the products as finally examined. The explosive reaction is com¬ 
plex in many cases, and the physical and chemical transformations 
through which the resultant products pass under various con- 


Explosive Reactions 


i 7 


ditions as the reaction progresses are but imperfectly known. 
The final products themselves are capable, in some explosives, of 
a considerable variation depending upon the conditions surround¬ 
ing the reaction, especially when, in oxygen-carrying explosives, 
there is not sufficient oxygen for complete combustion. 

The principal gaseous products of the explosives more com¬ 
monly used are carbon dioxide, carbon monoxide, water, nitrogen 
and nitrogen oxides, hydrogen, methane and hydrogen cyanide. 
Some of these gases are suffocating, others actively poisonous. 
The gases from propellent explosives are rarely dangerous since 
they usually escape at once into the open and are dissipated and 
diluted with air. Generally speaking, the commonly used high 
explosives not only produce a larger proportion of noxious gases, 
but their normal conditions of use tend toward a lingering pres¬ 
ence of the fumes. Thus in mine and quarry operations the 
gases are imprisoned more or less and are given off slowly from 
the shattered material; whereas in military use shells filled with 
high explosives burst usually after penetration into confined 
spaces, whence the gases are not quickly evacuated; and the same 
conditions may apply to a vessel holed by a torpedo or mine., 

25 . Flame of explosion.—Explosion is nearly always accom¬ 
panied by flame due to the high temperature at which the reaction 
takes place. Some of the gaseous products of explosion are 
themselves inflammable or form explosive compounds with air. 
Among these are hydrogen, carbon monoxide, and methane, all 
of which occur in the gaseous explosion products of smokeless 
powders. The large volume of flame occurring at the muzzles of 
guns upon discharge is considered largely due to the rapid inflam¬ 
mation or explosion of these gases mixed with air. This second¬ 
ary reaction is not necessarily complete and portions of the ex¬ 
plosive mixture remaining in the bore of the gun, or blown back 
by adverse winds, have been known to be ignited by glowing or 
burning residue in the bore. If the breech of the gun is open the 
resulting explosion may transmit flame to the rear of the gun. 
This action has commonly been called flareback. Serious acci¬ 
dents due to the ignition from this cause of fresh charges of 
powder being served to the gun have led to the adoption of the 
various gas-expelling devices fitted to guns fired from closed 
compartments, more particularly on naval vessels. 


3 


i8 


Naval Ordnance 


26 . Flashless charges.—The advantages to be gained by reduc¬ 
ing or suppressing the flash of guns in military operations—dis¬ 
guising of the location of guns firing at night and avoidance of 
the effect of blinding glare upon operating personnel—have led to 
partially successful efforts to produce flashless charges. A num¬ 
ber of various additions to the charge have been used in different 
services for the purpose. They have usually been substances 
which would tend to lower the explosion temperature or would 
be dispersed throughout the gases in a fine dust. A usual result of 
suppression of flash by such means is an increase in the volume of 
smoke. The desired reduction of flash is secured more easily in 
low-powered than in high-powered guns. A number of theories 
have been put forward to account for the extinction of flash by 
these means, none of which are general in their application or 
have found general acceptance. 


CHAPTER II. 

SERVICE EXPLOSIVES. 

Section I.—Brief History of the Development of Explosives. 

27 . The chemical constitution and physical form of modern 
explosives and the methods employed in handling and making use 
of them have resulted from a gradual development such as has 
been characteristic of the progress of so many other of the useful 
arts. A brief review of the more important phases of the history 
of the explosives art will be given as an aid to clearer understand¬ 
ing of the considerations which have governed the choice of the 
forms of explosive substances now used and their adaptation to 
present-day purposes. 

28 . Early incendiary substances.—Fire has, of course, been 
used as a weapon of war since the earliest recorded time and the 
transition from the use of ordinary combustibles to materials and 
mixtures of greater incendiary efficiency was a natural conse¬ 
quence of the gradual advance in physical and chemical knowl¬ 
edge. In the defense of Constantinople against the Moslems in 
the 7th and immediately succeeding centuries, the Greeks made 
very effective use of the so-called “ Greek tire,” particularly in 
naval engagements. This material was projected in flaming 
streams from tubes carried in the bows of the Greek vessels. It 
seems to have consisted of petroleum oils with the addition, per¬ 
haps, of sulphur. Similar materials were used both in streams of 
flame and in missiles by the Moslems during the Crusades, and 
knowledge of their use thus spread to other countries. Incendiary 
mixtures of this type were known during the Middle Ages as 
“ sea fire ” and “ wild fire.” The early incendiary weapons were 
the forerunners of the modern flame thrower. 

29 . Black powder.—When the properties of saltpetre, or 
potassium nitrate, became widely known, in about the 13th cen¬ 
tury, this substance was added to the earlier mixtures and a close 
approach was made to gunpowder. Charcoal soon came into use 
as the carbon-carrying constituent and the evolution of gunpowder 

19 


20 


Naval Ordnance 


was then complete. The use of saltpetre in incendiary mixtures 
seems to have been introduced by the Arabs and the Chinese at 
about the same time during the period referred to above. Knowl¬ 
edge of these mixtures, their uses and methods for their manu¬ 
facture spread rapidly, especially after the first firearms were 
made, early in the 14th century. 

The gunpowder of these early times was, in its proportions as 
well as in its ingredients, much like the black powder in use 
to-day. Its history, through the centuries in which it remained 
the only widely known and used explosive, records development 
through changes of form and of methods of manufacture, rather 
than of chemical constitution. It was at first a very fine mealy 
powder. Later it was formed into rough grains, separated and 
graded into various sizes by sifting. Still later, compactness of 
the grains was secured by forming the powder into cakes under 
a considerable pressure before breaking it up into grains. 

For a long time gunpowder was used only as a propellant in 
small arms and in cannon. It then was turned to account in blow¬ 
ing up enemy fortifications and later for more peaceable forms of 
blasting. After powder-train fuses had been successfully made, 
it came into use as a bursting charge for projectiles. 

In the early firearms, including cannon, the powder charge was 
ignited by the application of an open flame to a priming hole. 
The flintlock of the 18th century gave the first important improve¬ 
ment in methods of ignition. In this device the priming charge 
was ignited by sparks struck by the impact between flint and steel. 
Improved firing locks and the introduction of mercury fulminate 
came early in the 19th century and modern means of ignition have 
followed directly from them. Fulminate mixtures, in caps struck 
by a firing pin, or in containers where they are ignited by the 
heating of electric bridges, are still the most widely used means 
of initiating the action which results in the burning of the charge 
of propellent explosive in a gun, or the detonating of a high- 
explosive charge in a projectile, a torpedo, or a mine. 

Although the compression and granulation of black powder 
had given a partial improvement in its performance in guns, it 
remained difficult to regulate the action, especially in larger 
ordnance. In attempting to increase muzzle velocities to get 
greater range and penetrating power, it was found that the gun 


Service Explosives 


21 


chamber pressures soon became excessive because the powder 
burned too quickly. In i860 General Rodman, of the United 
States Army, realizing the advantages to be gained by increasing 
the time of burning of the charge, proposed the use of large grains 
of very dense powder for this purpose. As a result of his re¬ 
searches he also proposed that perforated grains be used in order 
that the burning surface of each grain might be increased as 
combustion proceeded. The use of grains such as developed by 
General Rodman gave means of regulating much better the 
ballistic action of black powders and such grains therefore came 
into general use. Various forms were common, such as the 
spherohexagonal and various prismatic shapes, including the 
hexagonal prism with a single perforation. The latter form was 
wddely used in large guns. The use of such grains was the first 
notable advance in securing a powder which would burn pro¬ 
gressively, that is, with increasing evolution of gases and heat. 

The last form of charcoal powder to be used in cannon was the 
“ brown ” or “ cocoa ” powder introduced about 1880. An under¬ 
burned straw charcoal was used in this powder and gave it the 
characteristic color from which it took its name. This charcoal 
gave a denser and hence slower burning structure to the powder 
and permitted better regulation of pressure. 

30 . Cellulose nitrates and smokeless powders.—In 1838 
Pelouze discovered that an explosive could be produced by nitrat¬ 
ing cotton, that is, by treating cotton with nitric acid in such a 
way as to cause NO, groups from the nitric acid, HNO ;j , to enter 
into combination with the cellulose of which the cotton is so 
largely composed. He thus produced cellulose nitrates, generally 
called nitrocellulose. His explosive was the first guncotton, but 
it was a very imperfect product and was not put to practical use. 
In 1845-46 Schonbein discovered that by nitrating cotton with a 
mixture of nitric and sulphuric acids an explosive of good quality 
resulted and that the nitration process could be controlled with 
some readiness. His process soon gained rather wide application 
since its importance in explosives manufacture was readily 
perceived. 

Manufacture of guncotton was undertaken in several European 
countries, but received severe setbacks through the occurrence of 
disastrous explosions in several factories in which it was being 


22 


Naval Ordnance 


made. The researches of various investigators, notably of Von 
Lenk in Austria and Abel in England, showed that the danger 
which had hitherto attended the manufacture of guncotton was 
due to the presence of impurities which could be removed by care¬ 
ful courses of treatment. The methods of purification which they 
introduced consisted principally in washing and boiling, together 
with pulping the material to facilitate cleansing. (See Art. 
42(e)). 

The earlier attempts to use guncotton as a propelling charge in 
guns were not successful. The velocity of the reaction was too 
great to permit of controlling the pressures, which were such as to 
burst many guns in which the explosive was used. Various 
measures were taken to retard the combustion, and cellulose 
nitrate powders, which were partially suitable for use in small 
arms, were produced by various makers. The solubility of cellu¬ 
lose nitrates in a mixture of ether and alcohol was noted by 
several who investigated its properties. The first to make suc¬ 
cessful application of this property of the material in producing 
a satisfactory propellent explosive was the French chemist Vieille, 
to whom was due a large part of the advance in knowledge of 
explosives. By thorough mixing of the nitrated cotton and the 
solvent he produced a gelatinous mass or colloid, which became 
quite hard and dense when the solvent was evaporated out. The 
resulting substance burned progressively and at moderate rates. 
The colloid was capable of being worked into the desired shape 
before drying and its formation into grains or strips to secure 
control of its burning was made possible. Adeille’s first powder of 
this kind, called Poudre B, was made in 1884. The improvements 
which have been made in smokeless powders since that time have 
been principally in the direction of better methods of purification 
and other measures for insuring chemical stability, although the 
technique of each of the other steps in the manufacturing process 
has also progressed in efficiency. 

31 . High explosives.—Nitroglycerine was discovered by 
Sobrero in 1846, but its highly explosive properties were not 
turned to account until Nobel, about i860, found that it could be 
detonated by means of a small charge of fulminate of mercury. 
Nobel found also that nitroglycerine could be used effectively 
and with much greater safety when mixed with various absorbent 



Service Explosives 


23 


materials. He began the manufacture of such mixtures, which 
have developed into many forms and have become widely known 
and used under the general name of dynamites. 

1 he nitration of cellulose and of glycerine to form powerful 
explosive substances led quickly to the discovery of a number of 
other explosives produced by the nitration of hydrocarbons, par¬ 
ticularly of the aromatic hydrocarbons found in coal tars. One 
of the earliest additions to the list was picric acid, which had been 
known as a dyestuff long before its explosive properties were 
discovered and employed. Others have followed in great number 
and variety. 

Mixtures of various high explosive compounds with other sub¬ 
stances, usually oxygen carriers, have also been developed and 
used, mostly for commercial purposes. The variety of widely 
known and used explosive substances has now become so large 
that the military explosives to be discussed in tbe remainder of 
this chapter comprise only a limited portion of the explosives 
field. 

Section II.—Explosive Substances: General Characteristics. 

32 . In the preceding chapter we have defined explosive sub¬ 
stances and discussed the general characteristics of the reactions 
to which they give rise. In this section we will consider the 
characteristics of the explosive substances themselves and of the 
materials from which they are made. 

33 . Explosive mixtures and explosive compounds.—Regarded 
from the point of view of their composition, explosives may be 
divided into two classes: (1) explosive mixtures, (2) explosive 
compounds. 

Explosive mixtures consist of an intimate mixture of distinct 
substances, properly prepared and conglomerated mechanically 
in varying proportions. Such explosive mixtures must have at 
least some oxygen supplier, such as a nitrate or chlorate, and some 
combustible, such as carbon or sulphur. Black and brown pow¬ 
ders are typical examples of such mechanical mixtures. 

Explosive compounds consist of substances whose molecules 
contain within themselves the oxygen, carbon, and hydrogen 
necessary for combustion. They are true chemical compounds 
and are therefore homogeneous in constitution. They have weak 


24 


Naval Ordnance 


molecular bonds, due to the presence in their molecules of weak 
bonding radicals, such as N 0 2 . They are therefore in a state of 
unstable chemical equilibrium. 

Mechanical mixtures can be graded by varying the propor¬ 
tions of the ingredients. The elements constituting an ex¬ 
plosive compound are always present in the molecule in the 
same quantities, according to the law of fixed proportions; 
therefore the nature of the explosive cannot be graded by vary¬ 
ing the quantities of the constituent elements as in the case of 
mechanical mixtures. It is to be noted, however, that the same 
initial substance may, in many cases, yield different explosive 
compounds by nitrating to different degrees. The different prod¬ 
ucts are, however, generally distinct chemical compounds. 

The explosive compounds consist very largely of nitrated hydro¬ 
carbons. The nitration results in the introduction of NO, groups 
into the molecules of the hydrocarbon. The nitration is almost 
always effected by treating with nitric acid mixed with sulphuric 
acid. Most of the explosive compounds which are nitrated hydro¬ 
carbons are derived from hydrocarbons of the aromatic series. 
Most important of these basic hydrocarbons are benzene, toluene, 
xylene, naphthalene, anthracene, and their derivatives, all of 
which are found in the coal tars resulting from the distillation of 
coal to produce coke. Among the principal explosives derived 
from the aromatic hydrocarbons are trinitrotoluene and picric 
acid, together with the picrates. Of the explosive compounds 
derived by nitration of non-aromatic hydrocarbons, the most im¬ 
portant are the cellulose nitrates and nitroglycerine. 

34. Uses of military explosives.—Viewed from the standpoint 
of the military uses to which they are put, explosives may be 
divided into three classes : 

(1) Burning, progressive, or propellent explosives (low ex¬ 
plosives'). In this class are included all powders used to propel 
projectiles from guns. 

(2) Detonating or disruptive explosives (high explosives). 
I his class includes the explosives used for bursting projectiles 
and for the main charge in torpedoes, mines, aero-bombs, and for 
most demolition purposes. 

( 3 ) Detonators or exploders. These are high explosives used 
in small quantity to initiate explosive reactions in charges of 
explosives belonging to the two classes above. 


Service Explosives 


25 


35. Propellants. —Smokeless powders of one form or another 
are now used almost universally for propellent charges. For 
military purposes, especially for guns larger than small arms, they 
may be considered to be of two classes, (a) single base powders 
and (b) double base pozvders. In the “ single base powders,” 
cellulose nitrates, which will hereafter be referred to as nitro¬ 
cellulose, form the only explosive ingredient. The other materials 
present in single base powders are present to give suitable form 
and stability to the powder. In the “ double base powders,” nitro¬ 
glycerine is present to assist in dissolving the nitrocellulose during 
manufacture, as well as to add to the explosive qualities of the 
powder. 

The single base nitrocellulose powders contain proportion¬ 
ately less oxygen than the double base powders. The resultant 
gases from the single base powders contain therefore relatively 
less of carbon dioxide, C 0 2 , and relatively more of carbon 
monoxide, CO, than do the double base powders. The heat 
liberated by equal weights of the two powders is therefore greater 
in the case of the double base powders, since the heat of forma¬ 
tion of CO, is greater than the heat of formation of CO. The 
conversion of carbon to carbon monoxide produces a greater 
volume of gas than its conversion to carbon dioxide. The single 
base powder therefore produces a greater volume of gas, though 
less heat than the double base powder. From a thermodynamic 
standpoint, it is therefore somewhat less efficient, but it has the 
advantage of causing less erosion in the gun because the resulting 
temperatures are lower. (See Art. 180.) 

Single base powders are used in France and in the United 
States. Double base powders containing nitrocellulose and nitro¬ 
glycerine are used in England, as “ Cordite,” in Italy, in Spain, and 
various other countries. 

36. Igniters. —Charcoal powders are now no longer used as 
propellants in military rifles. In the form of black powder, they 
are now used to facilitate ignition of smokeless powder charges, 
since they themselves are more readily ignited; in fuses, to propa¬ 
gate flame from one part to another; for saluting charges; for 
bursting charges in certain classes of projectiles; and for various 
other purposes. 


26 


Naval Ordnance 


37 . Detonating charges.—Large charges of high explosives 
are used as the main charges of torpedoes, mines, aero-bombs, 
and various classes of projectiles. I be explosive most commonly 
used for these purposes during recent years has been trinitroto¬ 
luene, generally known as TNT. Ihis material has also been 
called trinitrotoluol, trotyl, trinol, trilite, tritolo, and by various 
other names. For a number of years prior to the W orld War, 
guncotton was the preferred explosive material for torpedoes and 
mines, whereas picric acid or its derivatives were used commonly 
for the bursting charge of projectiles. TNT has practically sup¬ 
planted guncotton because of its greater safety, stability, and con¬ 
venience. It has also replaced picric acid and the picrates for 
filling certain classes of projectiles, especially those not intended 
for piercing armor plate. 

TNT was used in such quantities during the war that shortages 
in the materials required for its manufacture were threatened. 
This led to efforts to find satisfactory materials which could be 
mixed with TNT in order to conserve the available supply and yet 
secure powerful explosive mixtures. These efforts led to the 
adoption in various services of such explosives as amatol and 
sodatol, which consist of mixtures of TNT with ammonium 
nitrate and sodium nitrate, respectively. 

The material adopted by the United States Navy for mixing 
with TNT was trinitroxylol, or TNX, which is closely related to 
TNT. Xylene and toluene, the substances from which these ex¬ 
plosives are obtained by nitration, are, as previously mentioned, 
both derived from coal tar. 

Picric acid and the picrates are still largely used as"- bursting 
charges for projectiles since they possess advantages over TNT 
for certain classes of projectiles. They are preferred for armor¬ 
piercing projectiles because of the fact that they do not deflagrate 
or give incomplete explosions in passing through armor plate as 
readily as does TNT. Since an armor-piercing projectile will be 
more effective when bursting inside an armored structure after 
penetration than when bursting in passing through the armor, 
the characteristic discussed above becomes of much importance 
in selecting bursting charges. Picric acid and its derivatives have 
been used in various countries under the name of lvddite 
(English), melinite (French), explosive D (United States), 


S K RVIC E E XPLOSIVES 


^7 

shimose (Japanese), and ecrasite (Austrian). TNT has been 
used extensively as the bursting charge in high-explosive pro¬ 
jectiles not intended to be fired against armor. 

The general requirements of high explosives for projectiles, 
applying particularly to armor-piercing projectiles, are given 
below: 

(1) Should be reasonably safe to manufacture, and free from 
injurious effects to the operators as far as possible. 

(2) Must show a safe degree of insensitiveness in ordinary 
handling. 

(3) Must withstand the maximum shock of discharge from the 
gun under repeated firings in the projectile for which it is 
intended. 

(4) Must withstand the shock of impact without explosion 
when fired in fused projectiles against the strongest plate that the 
projectile alone will perforate without breaking up. 

(5) Must be uniformly and completely detonated with the 
service detonating fuse. 

(6) Should possess the greatest explosive power compatible 
with other necessary requirements. 

(7) Must not decompose when a dry or wet sample is hermeti¬ 
cally sealed and subjected to a temperature of 65.5° C. for one 
week. 

(8) Should be non-hygroscopic, and must not have its facility 
for detonating affected by moisture that can be absorbed under 
ordinary atmospheric conditions of storage and handling. 

High-explosive charges are usually loaded by melting and 
pouring if the kind of explosive substance used permits of this 
treatment. This gives greater density to the charge and hence 
greater explosive effect in a container of given volume. TNT 
lends itself especially to the casting of charges. 

38 . Detonators.—A discussion of the function of detonators, 
including boosters, was given in the preceding chapter. Deto¬ 
nators are of a great variety, in both mechanical and explosive 
details. The detonating materials used in detonators and boosters 
are chosen for their efficiency in detonating the explosive sub¬ 
stances of which the main charge is composed. The detonating 
reaction itself begins with a small charge of fulminate or fulmi¬ 
nate mixture and is transmitted through the booster to the main 


28 


Naval Ordnance 


charge. The substances now most commonly used for the deto¬ 
nating trains and for boosters are tetryl, picric acid, and crys¬ 
talline TNT. 

Section III.—Manufacture and Characteristics of Service 

Explosives. 

39 . In this section will be given brief notes on the manufacture 
of certain explosives now used in the United States Navy, with 
further reference to the properties and characteristics of each. 
Inasmuch as the details of manufacturing methods and equip¬ 
ment change somewhat from time to time and vary to some 
extent between different manufacturers, such details will in gen¬ 
eral not be given fully. Attention will be directed more closely 
to the principles followed in manufacture and the precautions 
taken to insure safety in manufacture and purity and stability of 
the product. 


(i) SMOKELESS POWDER. 

40 . The smokeless powder used by the United States Navy is a 
uniform ether-alcohol colloid of carefully purified nitrocellulose. 
A small quantity of diphenylamine is added in the course of manu¬ 
facture to assist in preserving the chemical stability of the powder. 
The powder is made to conform to very rigid manufacturing 
specifications, which insure a very pure product, and to rigid 
ballistic specifications, which insure uniformity of performance 
in the gun. Except for minor differences in specifications, the 
same kind of powder is used by the United States Army. 

41 . Raw materials.—The principal raw materials used in the 
manufacture of United States Navy smokeless powder are the 
following: 

(a) Cotton. — the cellulose material to be nitrated consists of 
bleached and purified unspun cotton wastes or short-fibered cotton, 
the latter being obtained through the removal of the fiber ends 
which are found adhering to the cotton seed after the ginning 
process. Short-fibered cotton is particularly suitable for nitra¬ 
tion because the nitrating acids can reach all parts of it readily, 
which tends to uniformity in nitration. 

The purification to which the cotton has been subjected before 
it is received at the powder factory consists usually in boiling with 


Service Explosives 


29 


caustic soda to remove impurities, especially the waxy constituents 
of the fiber, and to make those which remain more readily remov¬ 
able in the purifying processes undertaken later during the course 
of manufacture. The cotton is then bleached with chlorine, 
washed, and dried! 

(b) Acids.—A mixture of nitric and sulphuric acids is used in 
the nitrating process. Mixed acids as made or received at the 
factory are required to conform to rigid specifications as to purity 
and strength. The mixture as received has a total acid content of 
about 95 per cent and the proportion of nitric and sulphuric 
acids is about equal. The acid as used directly in the nitrations 
is mixed with weaker acids which have been used in previous 
nitrations, in which they have lost a part of their acidity. These 
weaker recovered acids are known as spent acids and the process 
of mixing them with the fresh acid mixture is known as fortifying 
the spent acids. The usual acidity of the nitrating mixture is 
about 85 per cent, but this is varied somewhat with changing con¬ 
ditions, especially with changes in temperature. The proportion 
of the acid constituents is about two parts of nitric acid to one of 
sulphuric acid, by weight. 

(c) Ether and Alcohol.—A mixture of ethyl ether and ethyl 
alcohol is used as a solvent for the nitrocellulose, as will be de¬ 
scribed later. They are required to be of a high purity. 

(d) Carbonate of soda.—Carbonate of soda is used in the 
water in which the nitrocellulose is boiled during certain stages of 
the purification process. It also is required to be of a high degree 
of purity. 

(e) Diphenylamine.—Diphenylamine, a pale yellow crystal¬ 
line organic substance with a slightly alkaline reaction, is incor¬ 
porated with the powder in order to neutralize any acid products 
which might be formed in the powder as a result of gradual 
decomposition. Diphenylamine thus arrests decomposition and 
hence adds to the chemical stability of the powder. It is therefore 
called a “ stabiliser Other substances with similar chemical char¬ 
acteristics and reaction are available as stabilizers and have been 
used in various countries. 

42 . Steps in manufacture.—The following description of the 
processes by which United States Navy smokeless powder manu¬ 
facture is carried out represents general or typical processes. As 


30 


Naval Ordnance 


previously pointed out, the details of the equipment and procedure 
differ slightly with various manufacturers. 1 he principles fol¬ 
lowed and the principal steps necessary are, however, the same 
for all. 

(a) Picking of cotton.—The purified cotton as received at the 
powder factory is picked by machine to loosen it and to permit 
removal of possible small bits of foreign matter which may have 
escaped previous inspections. Long-fibered cotton and short- 
fibered cotton are treated differently in the picking process, the 
former being combed or carded in a mill having toothed rolls, the 
latter being ground between corrugated plates. The picked 
cotton, in both cases, passes from the picker to a bin from where 
it is taken to the dry-house in canvas bags. 

(b) Drying.—The cotton is dried to a moisture content of less 
than i per cent before nitration. Moisture in the cotton during 
the nitration process would tend to non-uniformity of nitration 
and increase the danger of burning the material due to the heat 
evolved by the interaction of the acids and the moisture. The 
cotton is dried by passing on a belt conveyor through an enclosed 
drying chamber through which air heated to too° C. is circulated. 
In another drying system sometimes used, the cotton is dried in 
large bins with wire mesh bottoms, lined with burlap. Air heated 
at about ioo° C. is passed through the cotton, being driven 
through ducts to the bins by a fan blower. The usual time of 
drying by these systems is about 1 2 hours. 

(c) Mixing acids.— The acid mixture used in nitration is 
obtained by fortifying spent acids as already described. The 
amount of fresh acid mixture to be added is calculated from 
chemical analysis of samples taken from each tank of spent acid. 
The fortified mixture is brought to a temperature of about 30° C. 
in heating tanks before delivery to the nitrators. 

(d) Nitrating.—The first stage of the nitration consists in the 
immersion of a charge of dried cotton in the heated mixed acids. 
The various nitrating processes dififer principally in the nature 
of the equipment used for this immersion and the subsequent dis¬ 
posal of the spent acids and nitrated cellulose resulting. In one 
process generally used, about 1500 pounds of the fortified acid 
mixture is run into an iron pot in which means for stirring the 
charge are provided, generally by power-driven paddles. About 


Service Explosives 


3' 


30 pounds of cotton is immersed in the pot and the mixture of 
acids and cotton is stirred during the time the acids are acting 
upon the cotton. Means are provided for carrying off the fumes 
resulting from the reaction. About 20 minutes suffices for the 
reaction, at the end of which time the cotton has been nitrated to 
the required degree, when it contains 12.60 ±0.10 per cent of 
nitrogen. At the end of this stage the cotton and acids are run off 
into a centrifugal wringer, which is a perforated iron basket upon 
a central shaft with means for rotating at high speed. The basket 
is surrounded by an iron casing in which are provided drain out¬ 
lets for the running off of the spent acids which are removed from 
the charge by centrifugal force due to the rotation. The inner 
basket permits the acids to pass through but retains the nitrated 
cotton. After the wringing is complete the nitrated cotton, which 
will hereafter be called pyrocellulose or pyro, is drawn off into a 
basin where it is immediately immersed in fresh water. 

In certain cases, the nitration and wringing are both carried out 
in the centrifugal wringer. In another process, known as the 
displacement process, the nitration is carried out in a pan, in which 
the mixture of cotton and acids stands quietly until the nitrating 
reaction is complete. At the end of this time the spent acids are 
carried off by running cold, fresh water into the charge and 
allowing the spent acids to run off simultaneously as they are dis¬ 
placed by the water, the volume of material in the nitrating pot 
being kept constant. 

The chemical processes taking place during the nitrating reac¬ 
tion are not entirely clearly defined. It has been generally accepted 
that the first action is a conversion of the cotton into cellulose 
sulphates by the action of the sulphuric acid, with the liberation 
of water. The nitric acid acts upon the cellulose sulphates so 
formed, displacing the sulphuric acid constituents and producing 
cellulose nitrates. The sulphuric acid liberated in this reaction 
combines with the water resulting from the previous reaction to 
form hydrates. The replacement of cellulose sulphates by cellu¬ 
lose nitrates is not complete and a certain portion of the sulphates 
remain as impurities, to be removed in the subsequent purification 
processes. 

(e) Purifying.—The first step in the purification process takes 
place in the immersion basin previously Inentioned. 


32 


Naval Ordnance 


(1) Drowning.—In transferring the pyro from the wringers 
the transfer is carried out as quickly as possible and the pyro is 
immediately immersed, or drowned, in water. If the pyro should 
be exposed to the air for any considerable period, it is likely to 
take fire through the action of the nitrating acids not completely 
removed in the wringing process, and to burn slowly with an evo¬ 
lution of dense nitric fumes. In the displacement process referred 
to above such burning cannot occur, as the pyro is completely 
immersed during the time the acids are being replaced with water. 
When the wringer process is used the pyro, after being trans¬ 
ferred to the immersion basin, is run thence by pumps or by 
gravity to boiling tubs where the next step in purification is carried 
out. During this transfer the pyro is still completely immersed 
and most of the free acids remaining in the pyro as it comes from 
the wringer pass off into the water. 

(2) Preliminary boiling.—The boiling tubs are large wooden 
tanks fitted with feed pipes and drain pipes for the admission and 
draining off of water, and with perforated wooden false bottoms. 
The perforations in the inner botton of the tub permit the passage 
of water, but hold the pyro. Into the space betwen the false 
bottom and the bottom of the tub is led a steam supply pipe which 
is perforated for the admission of steam into the water contained 
in the enclosed space. The pyro is protected from direct contact 
with the steam pipe, which is encased in a wooden trunk, except 
for the portion which lies under the perforated false bottom. The 
tub is nearly filled with fresh water, in which the pyro is immersed, 
and the steam is turned on. The temperature is gradually raised 
to 8o° C. for a short time, when the steam is turned off and the 
water drained from the tub. A fresh supply of water is run in, 
heated to ioo° C. by the steam, and the boiling is continued for 
about four hours. This boiling is repeated several times, the 
water being changed in each instance. 

(3) Pulping.—After the preliminary boiling the pyro passes 
to pulpers, where it is finely ground to permit the next step in 
purification to reach all parts of the fiber, and to reduce it to a 
consistency which is desired in the later operations. 

The pulper usually used is nearly the same as is used in many 
paper mills for the pulping of rags. It is a long tank, with a cast- 
iron roller carried in a horizontal position near the middle of the 


Service Explosives 


33 


pulper. Above and below the roller are concave plates which fit 
the roller, with very small clearances, throughout its length and 
over an arc of about 20° at top and bottom. The roller and the 
plates have sharp longitudinal ribs or knives which cut and grind 
the pyro passing between them. The pulper is kept nearly full of 
water and is fitted with baffle plates to direct the circulation of the 
water and pyro in such a way that they pass first under and then 
over the rotating roller. A bailer is provided to permit of chang¬ 
ing the water during the pulping operation. The bailer consists 
of a hexagonal frame, the sides of which are covered with a fine 
screen, which permits water to pass through into the inside of the 
bailer and thence to an exhaust pipe, but does not allow the pyro 
to pass through. 

The pulping operation is usually completed in about eight hours. 
The water and pyro from the pulpers are run through a pipe line 
to the poachers, in which the final step in purification takes place. 
Before passing into the poachers the water and pyro pass through 
a very fine screen or filter which rejects the particles of pyro 
which are still too coarse. This part of the pyro is returned to 
the pulpers. 

(4) Poaching.—The poachers are large cylindrical wooden 
tubs similar to the boiling tubs. They are fitted with intakes and 
outlets for pyro and water, water supply pipes, and perforated 
steam pipes protected by a baffle. There is also a set of paddles 
carried by a rotating vertical shaft in the center. In the poachers 
the pyro is boiled, by the action of steam admitted through the 
steam pipe, and is stirred constantly by the paddles. In the first 
boiling carbonate of soda is usually added to the water to assist 
in purification. The operation continues about six hours, when 
the pyro is allowed to settle for one hour, the water is replaced by 
fresh water and the boiling is repeated for two hours, and then 
for four one-hour periods, the water being changed after each 
boiling as described above. The water is changed again after 
the last one-hour period of the boiling and the pyro is washed by 
stirring without heat for half an hour. It is allowed to settle for 
one hour, when the water is changed and the washing repeated. 
Ten such washings are given. No carbonate of soda is used after 
the first boiling. 

After this course of purification is completed a sample of the 
pyro is taken from the poacher and given the prescribed chemical 
4 


34 


Naval Ordnance 


tests for stability. If it is sufficiently pure to pass these tests, it is 
run out of the poacher to a centrifugal wringer where much of the 
water is removed from it. If it does not pass the chemical test, 
it is given further treatment in the poachers to increase its purity. 

(f) Dehydrating.—From the wringers the pyro, containing 
still about 40 per cent of water, passes to the dehydrating house. 
Here the remaining water is forced out of it by forcing alcohol 
into it under pressure. A charge of about 50 pounds of pyro is 
loaded into the cylinder of a hydraulic press, where it is sub¬ 
jected to a pressure of about 200 pounds per square inch. This 
compression takes place between two pistons entering the cylinder 
from opposite directions. The upper piston is raised and alcohol 
is run in on top of the pyro cake. Air under about 75-pounds 
pressure is admitted over the alcohol, which is forced through the 
cake, leaching the water out of it. The cake is then given a final 
pressing between the pistons, to remove the excess alcohol. The 
amount of alcohol then remaining is approximately that desired in 
the ether-alcohol solvent. 

(g) Mixing.—The compressed cake of pyro from the dehy¬ 
drating press is taken to the mixing house in a metal can. Here 
it is broken up in a mixer, which is a water-jacketed iron con¬ 
tainer, with electrically driven rotating screw paddles inside. It 
is practically the same as the dough mixers used in bakeries. The 
pyro containing alcohol is mixed for about 20 minutes in order to 
break it up thoroughly. The ether constituent of the solvent is 
then added, in about twice the amount of the alcohol constituent 
already present. 1 he stabilizing substance, diphenylamine, is also 
added at this stage, being dissolved in the ether before the ether 
is poured into the mixer. 1 he weight of diphenylamine added 
amounts to about 0.45 per cent of the dry pyro and about 0.4 per 
cent of the finished powder. 

The charge is then mixed again for about 30 minutes. During 
this time the pyro becomes partially dissolved or colloided by the 
ether-alcohol mixture. It is formed into a cylindrical cake or 
block in a hydraulic blocking press and passes then to the strain¬ 
ing presses. 

(h) Pressing.— 

(1) Strainer presses.—The colloid block is placed in a strainer 
press whose bottom plate is perforated with 3/32" holes. The 


Service Explosives 


35 


colloid is forced through these holes under a pressure of about 
1300 pounds per square inch applied by a piston descending from 
above. The colloid emerges in small cords much like macaroni. 
This press is therefore frequently called the macaroni press. The 
pressing and straining the colloid receives here gives it a more 
thorough mixing and greater homogeneity. The colloid as it 
emerges from the strainer press is a rather tenacious translucent 
material which has a uniform consistency. The cords of the 
colloid pass from the strainer press into a blocking press, directly 
below, and are again pressed into a block. 

(2) Die presses.—The die presses in which the colloid is 
formed into powder grains are similar to the strainer presses, 
except that they are placed horizontally. In the die press the 
colloid is forced through a die carried in a diaphragm at the end 
of the press. The die consists of a tubular channel, the outside 
opening of which is somewhat smaller than the inner one. In the 
inner end of the die is a very small perforated plate which carries 
long pins which give the finished grain its perforations. In some 
of the smaller granulations there is only one centrally placed pin 
in the die and hence only one perforation in the finished grain. 
For the larger powders there are seven pins in the die. one in the 
axis of the die and the other six spaced equally about it, and 
equidistant from each other. 

The colloid block from the blocking press is placed in the die 
press and pressure is applied to force the colloid through the die. 
This pressure is usually from 1800 to 2500 pounds per square 
inch, depending upon the consistency of the colloid and the size of 
the die. Under this pressure the colloid is forced through the 
small perforated diaphragm and then closes in around the pins. 
It issues from the face of the die in a continuous longitudinally 
perforated cord, which is led to a machine cutter and there cut by 
revolving knives into the desired uniform lengths. The cord of 
powder passing from the die to the cutter is inspected for im¬ 
perfections. If these are found, the imperfect section is broken 
out of the cord by hand and discarded. The grains falling from 
the cutters are also inspected and any distorted or faulty grains 
are removed. 

The “ green ” powder as it comes from the die press is fairly 
soft because of the large excess of solvents which it contains. 


36 


Naval Ordnance 


When the solvents are evaporated out the grains become hard and 
translucent; in physical characteristics they are then much like 
horn. 

(i) Recovery of solvents.—The first step in the drying of pow¬ 
der consists in rapid heating in a closed container to evaporate a 
portion of the excess solvents, which are then recondensed for 
further use. This process is generally called solvent recovery. 
There are several different forms of apparatus used for this pur¬ 
pose, but the principle is the same in all cases. After the green 
powder has been charged into the recovery container, a current of 
preheated air is passed through the powder and a part of the 
excess solvents are quickly volatilized. The air then passes 
through a Cooling system where the vaporized solvents are con¬ 
densed and are drawn off as liquid, to be separated into ether and 
alcohol by distillation. Most of the solvent thus recovered is 
ether, since that is more volatile than alcohol. The air, after 
being cooled to condense the solvents, passes again through the 
preheaters and so once more through the cycle. The temperature 
of the air passing through the powder during recovery of solvents 
Varies from about 35 0 C. to 39 0 C. The powder is subjected to 
the process for four or five days. 

(j) Drying.—The final drying of the powder is usually carried 
out by a gradual process of air drying in large dry-houses. There 
are several different types of dry-houses, but all are so designed 
as to permit the maintaining of a constant temperature and a con¬ 
stant circulation of air. The powder is placed in bins through 
which air is circulated. During the first 60 days the powder is 
dried without heating. The temperature of the circulating air is 
then raised usually to 40° C. and maintained at that temperature 
during the remainder of the drying period, which may continue 
through two to four months longer. The duration of the drying 
period will depend upon the total amount of volatiles to be evapo¬ 
rated from the powder, and upon the size of the grain. The per¬ 
centage of total volatiles remaining in the powder is determined by 
analysis from time to time, as the estimated completion of drying 
approaches. When the total amount of volatiles has been reduced 
to the proper figure, the grain will have been dried to the desired 
dimensions and speed of burning. The powder shrinks materially 
during drying and this must be taken into account in determining 

o 


Service Explosives 


37 


the dimensions of the die in which the grain is formed in the 
pressing operation. The final dimensions of the grain exert an 
important influence upon the ballistic characteristics of the powder 
in a given gun. This point will be referred to again later. 

The percentage of volatiles remaining in each powder after 
drying varies from about 3 per cent to 7 per cent, being greater 
in the larger granulations. 

Water-dried powders.—Nitrocellulose smokeless powders can 
also be dried, that is, have their excess volatiles removed, by cir¬ 
culating through them warm water instead of warm air. The 
temperatures used in water drying are somewhat higher than in 
air drying, and the process is completed much more quickly. A 
short air drying suffices after the water treatment is completed. 

(k) Blending.—The poacher lots maintain their identity until 
they have passed through the dry house. For convenience in 
assigning powders to ships, and for the maximum uniformity in 
the charges assigned to each ship, it is desirable to reduce as much 
as possible the number of lots or indexes of powder. Each index 
consists of 100,000 pounds of powder for guns above 3", and 
usually of 50,000 pounds for 3" and smaller guns’. In order to 
make up one index, it is therefore necessary to use a number of 
poacher lots, and these must be blended in order to give uni¬ 
formity throughout the index. 

After the drying is completed and before blending, the powder 
is exposed to the atmosphere for from 24 to 60 hours in order to 
insure that surface moisture is as nearly uniform as possible. 

Blending is usually carried out in blending towers. The tower 
consists of a series of bins arranged in groups, with groups one 
above the other. The bins of each group are usually arranged 
in polygons and each bin has a trap or gate valve in the center of 
its group. In blending, the top group of bins is filled with pow¬ 
ders from different poacher lots. The traps or gate valves are 
opened simultaneously and the powder from the bins falls to the 
next group in one stream, which separates about equally into the 
bins of the next lower group. This operation is continued from 
group to group and the powder is finally drawn off through a 
hopper at the bottom of the blending tower into the powder boxes 
in which it is shipped to the ammunition depots. The boxes are 
usually run under the hopper on scales and are weighed as they 


38 


Naval Ordnance 


are tilled. They are then sealed with airtight covers and marked 
with the factory identification number, the weight and the date of 
packing. During the packing a firing sample is selected for proof 
of the lot in a gun of the type and caliber for which it is intended. 
If the lot passes proof and chemical specifications and is accepted 
by the Bureau of Ordnance, it is assigned an index number by 
the bureau. It retains that index number while it is in service. 

SUMMARY. 

The process of manufacture may be summarized as follows: 

(a) Picking. —To grind and to remove lumps and foreign 
matter. 

(b) Drying. —Dried for about 12 hours at about ioo° C. to 
reduce moisture contents to less than 1 per cent before nitration. 

(c) Mixing acids. —Fortifying “ spent acids ” to required 
strength before delivery to nitrators. 

(d) Nitrating. —Thirty pounds of cotton immersed in H 2 S 0 4 , 
and HN 0 3 for about 20 minutes, when it contains 12.60 ±0.10 
per cent of nitrogen. 

(e) Purifying. —(1) Drowning. —To remove free acids. 

(2) Preliminary boiling. —Boil at temperatures 8o° and ioo° C. 
to further remove free acids. 

(3) Pulping. —Ground for about eight hours in contact with 
water, to break up tubular cotton fibers. 

(4) Poaching. —Boiled in water with carbonate of soda for 
about six hours, allowed to settle one hour, then water is replaced 
with fresh water. The boiling is repeated for two hours, then for 
four one-hour periods, using fresh water for each boiling. 
Washed one-half hour and drained one hour (without heat), re¬ 
peated 10 times. After poaching a sample is sent to laboratory 
for testing. 

(f) Dehydrating. —Water is forced out of pyro by forcing 
alcohol into it under pressure. Charge is then caked under 
pressure. 

(g) Mixing. —A charge of dehydrated pyro is ground for 20 
minutes to break it up thoroughly. The ether constituent of the 
solvent and the diphenylamine are then added and charge mixed 
for 30 minutes. It is now a colloid and is again formed into cakes 
for next process. 


Service Explosives 


39 

(h) Pressing. — (i) Strainer presses. —Under a pressure of 
about 1300 pounds, the cakes are forced through 3/32" holes in 
strainer press. The cords as they issue pass directly to a blocking 
press below and are again formed into a block. 

(2) Die presses. —Under a pressure from 1800 to 2500 pounds, 
the cakes are forced through the die press, from which it emerges 
in rods of the desired diameter with seven perforations (one in 
small-grain powder). The rods, as they issue from press, are 
cut into grains of the desired length by revolving knives. 

(i) Solvent recovery. —The green powder is submitted to hot 
air for four to five days at a temperature of 35 0 C. to 39 0 C. The 
solvents having been vaporized are recovered by condensation. 

(j) Drying. —The green powder is dried at air temperature for 
about 60 days, and at 40° C. from two to four months. 

(k) Blending. —One hundred thousand or 50,000 pounds in one 
charge is blended to get all the powder of one index of an even 
mixture, so that any two bags of equal weight will give the same 
initial velocity under similar conditions. 

As the powder issues from the " blending tower” it is.weighed, 
boxed, and sealed with airtight covers and marked with a factory 
identification number, the weight, and date of packing. 

After proof, if satisfactory, an index number is assigned by the 
bureau. 

43 . Reworked powder.—Powders which have been subjected 
to conditions which have or may have impaired their stability, and 
remnants of indexes, are recovered for use as reworked powder. 

In reworking, the old powders are ground in water by a large 
heavy mill, which crushes the grains and finally reduces them to a 
pulp similar to the fresh pyro pulp coming from the pulpers. 
This reworked pyro, as it may be called, is put through the same 
general processes as new pyro, from the poaching on to the end 
of the process. Reworked powders are considered nearly as good 
as new powders, the principal difference being that their nitration 
is not quite so high, and the grains are not quite so tough. Re¬ 
worked powders are darker in color than new powders. 

44 . Smokeless powder—general discussion.—The smokeless 
powder resulting from the methods of manufacture described in 
the foregoing paragraphs is a hard, tough, translucent substance 
varying in color from a light lemon to a deep brown. The differ- 


40 


Naval Ordnance 


ences in color are clue to some extent to variations in manufacture 
and in the water used in the purifications processes. 

The nitrocellulose constituent of the powder is regarded as a 
mixture of ennea-nitrocellulose, C 24 H 31 O 20 (NO 2 ) 9 , and deca- 
nitrocellulose, C 24 H 30 O 20 (NO,) 10 . These nitrocelluloses are the 
highest which are soluble in the ether-alcohol mixture. 

The powder burns regularly and progressively, leaving an 
almost negligible quantity of asb. The progress of the reaction of 
the powder in a gun may be divided into three stages: ignition, 
inflammation, and combustion. 

(a) Ignition.—Ignition is the setting on fire of a part of the 
grain or charge. It results from the application of sufficient heat 
to raise the temperature of the powder to the point where rapid 
chemical decomposition takes place. When the powder is thus 
ignited, the reaction proceeds without further external aid and 
rapid evolution of gases, with heat and flame, results. The time 
necessary for ignition varies with the kind of powder and its con¬ 
dition. A dry powder ignites more readily than a damp powder; 
a rough grain more readily than a smooth grain. Black powder 
ignites more readily than smokeless powder, although its ignition 
temperature is higher. This is because the heat conductivity of 
smokeless powder is greater than that of black powder, and the 
local heating therefore takes place more slowly. For this reason, 
charges of smokeless powder are ignited through small ignition 
charges of black powder, the burning of which envelops the 
grains of the smokeless powder with an intense and somewhat 
sustained flame. The ignition charges themselves are ignited by 
a flame from a primer which is fired by electricity or by percus¬ 
sion. In cartridge-case guns the ignition charge of black powder 
is contained in a magazine attached to, or forming a part of, the 
primer proper. 

(b) Inflammation.—Inflammation is the spreading and de¬ 
velopment of the flame over the whole surface of the grain or 
charge. The burning of smokeless powder takes place always 
upon the surface, a new layer becoming ignited as the preceding- 
one burns away. Each charge or section of smokeless powder is 
provided with a sufficient ignition charge of black powder to 
produce throughout the powder chamber a volume of flame which 
will surround each grain of smokeless powder and inflame its 


Service Explosives 


4i 


surface. This inflammation is aided by the pressure due to the 
gases from the ignition charge. 

(c) Combustion.—Combustion is the burning of the inflamed 
powder from layer to layer upon the surface. In the absence of 
pressure, for instance in the open air, this combustion is very 
slow. When the powder is burned in a gun, or in other confined 
space, the combustion is greatly accelerated, as has previously 
been pointed out, due to the pressure of the resulting heated gases 
upon the surface of the grains. 

The rate of combustion depends not only upon the pressure of 
the gases surrounding the burning powder, but also upon the tem¬ 
perature of these gases. Their temperature depends upon the 
composition of the powder and the conditions under which the 
combustion takes place. The rate of combustion of dififerent 
powders varies also with the amount of residual solvent remaining 
in the powder after drying. The greater the percentage of 
volatiles, the slower is the rate of burning. 

The progressively burning quality of smokeless powder is made 
use of in controlling the evolution of gases, to get the desired 
regulation of pressures. This is done by varying the size and 
shape of the grains, which will determine the rate at which gases 
are evolved, other conditions being equal, since it is evident that 
with equal rates of combustion the rate of evolution of gases will 
be proportional to the area over which combustion is taking place. 

The desirability of having a form of grain which presents con¬ 
stantly increasing burning surfaces during the progress of com¬ 
bustion has previously been referred to. Solid grains give the 
least progressive form, since their burning surface constantly 
decreases as combustion proceeds inward from the surface. The 
best form of solid grain is a flat strip, since its burning surface 
decreases least rapidly. As previously stated, the form of grain 
adopted by the United States Navy to give progressive burning 
is the perforated cylinder. Cylindrical grains with single central 
perforation are used in many small-arms powders and powders 
for small-caliber guns. Single perforated grains have a prac¬ 
tically constant burning surface. A cylindrical grain with seven 
perforations arranged as previously described under the manu¬ 
facture of smokeless powder is used in the larger caliber United 
States Navy guns. The cross-section form of this type of grain 
is shown in Fig. A. 


42 


Naval Ordnance 


The principal dimension used in designing powder grains is the 
least dimension between burning surfaces. Since the burning 
takes place at equal rates in each direction, under equal conditions, 
the time taken to burn through this least dimension determines in 
general the time occupied by the combustion of the whole grain. 

/ 0 0 \ 

U-O'O o J 

loo/ 

Fir.. A. —Original Grain. 

1. Inner Web Thickness. 

2. Outer Web Thickness. 

This dimension is called the “ web thickness.” In solid grains the 
web thickness is the least dimension of the grain ; for single per¬ 
forated cylindrical grains the web thickness of ——- , where D 

^ 2 

is the diameter of the grain and d the diameter of the perforation. 
For multi-perforated cylindrical grains the web thickness is 

^ — 3 where D is the diameter of the grain and d the diameter 

4 

of the perforations. Multi-perforated cylindrical grains have an 
increasing burning surface, since combustion proceeds from the 
outer diameter inward, and from the perforations outward. These 



Fig. B.—Partly Consumed. 

Hatched Areas Show Slivers. 

grains therefore give progressively increasing volumes of gas up 
to the instant when the inner burning surfaces meet and the grain 
separates into solid slivers. 

Fig. B illustrates the progress of combustion in a multi-per- 



Service Explosives. 


43 


forated grain up to the instant when slivers are formed. From 
this instant the burning surface decreases and the powder burns 
less progressively. In firing reduced charges, sometimes used for 
target practice in order to reduce wear of the gun due to erosion, 
the combustion of the grain is often incomplete due to the lower 
pressures generated, and unburned slivers of powder are fre¬ 
quently found outside the gun, being blown out by the rush of 
powder gases when the projectile emerges from the muzzle. This, 
however, does not affect the uniformity of the pressures and 
velocities attained, since the effective combustion will have been 
completed when the projectile leaves the gun. 

By density of powder is meant its specific gravity, or the ratio 
of the weight of a given volume of powder to the weight of an 
equal volume of water, at the standard temperature. The density 
of large-grained powders may be determined by weighing a grain 
of the powder in air and in water. For small grains the mercurial 
densimeter may be used and correction applied to obtain weight in 
water, rather than in mercury. The difference of the weights in 
air and water is the weight of a volume of water equal to the 
volume of the grain. 

The density is then the weight in air divided by the difference 
of the weights. 

The density of smokeless powders varies from 1.54 to 1.62. 

The density of a grain of nitrocellulose powder is practically 
constant so long as it contains a uniform quantity of solvent and 
moisture. It has been found that the density or specific gravity 
varies inversely as the total amount of volatiles, and is represented 
by the following formula : 

Sp. gr._ I2 -37 2 ^ —013 2 T-V- or =1.672— (.0178xT. V.) (2) 

7-4 

where T. V. is the percentage of total volatiles. The curve is 
shown in Fig. C. 

Since the amount of remaining volatiles is greater for the larger 
web powders, in general the density of the powder may be said to 
decrease as the web increases. 

45. Products of combustion of nitrocellulose powder.—The 

decomposition of our nitrocellulose powders in burning is usually 
represented by the following equation : 

C 24 H 30 ( NO,) 10 O 20 = I2CO, 4 - 12CO -f-qHoO +1 iH + 5^2* 



44 


Naval Ordnance 


This represents a reaction which is complete for a nitrocellulose 
of 12.75 P er cen t nitration. It does not take into account the 
reactions due to the presence of the volatiles or the stabilizer. It 
is deduced from theoretical considerations and from the study of 
products of explosion made in laboratory apparatus in which only 
a small amount of explosive is used, the density of loading being 
therefore small, and in which the gases have been considerably 
cooled before examination. That the actual products of com¬ 



bustion differ considerably from those above represented is evi¬ 
denced by the deep orange-colored cloud of gas accompanying 
the discharge of the gun. This color is due to oxides of nitrogen, 
which are not accounted for in the theoretical equation. Since 
the actual products of combustion are not all colorless gases the 
powder cannot be called truly “ smokeless.” This term has been 
used in a relative sense to distinguish the modern powders from 
their predecessors which gave off dense clouds of white smoke. 
The gases from “ smokeless ” powders are much less opaque and 
are dissipated much more rapidly. A small cloud of white smoke, 











































Service Explosives 


45 


due to the black powder ignition charge, is usually readily dis¬ 
tinguished in the gas from a gun firing smokeless powder. 

It will be noted that carbon monoxide forms a considerable 
portion of the products of combustion in the above reaction. The 
effect of this upon the temperature of the gases during the ex¬ 
plosive reaction has already been pointed out, as has also the 
possibility of “ flareback ” due to ignition of this inflammable 
gas when mixed with air. 

46 . Stability of nitrocellulose powders.—Powders containing 
nitrocellulose are subject to a very gradual chemical decomposi¬ 
tion which may in time be a source of danger unless measures are 
taken to arrest or check such action. From its nature nitrocellu¬ 
lose is, like many explosive compounds, in a state of unstable 
chemical equilibrium and is readily acted upon unfavorably by 
impurities which may be present with it. If decomposition takes 
place in any particle the decomposition products will include nitro¬ 
gen oxides which have an acid reaction and will facilitate further 
decomposition. The reaction occurring will be accelerated for 
this reason and a progressive decomposition will result. The 
decomposition will be greatly facilitated by heat and by the 
presence of moisture. 

During manufacture every precaution is taken to insure the 
absence of impurities in the raw materials and the removal of 
impurities during the various courses of purification. The prin¬ 
cipal impurities removed during manufacture are the sulphates, 
which are formed as by-products, so to speak, of the nitrating 
reaction, and the free acids remaining after nitration. The addi¬ 
tion of the stabilizing substance, diphenylamine, is the means 
taken to counteract any decomposition which may begin in the 
finished powder. The way in which diphenylamine arrests de¬ 
composition through neutralizing the acid decomposition products 
has already been mentioned. Progressive decomposition cannot 
occur until all of the diphenylamine in the powder has been used 
up by combining with the acids. The use of diphenylamine has 
greatly increased the stability life of our powders and the limits 
of its effectiveness have not yet been reached. 

The presence of residual volatiles in the powder also tends to 
retard possible decomposition. For this reason, as well as to 
avoid change in ballistic qualities through change in the rate of 


46 


Naval Ordnance 


combustion, every effort is made to prevent the loss of volatiles 
from the finished powder. 

Excessive heat will have a most unfavorable influence upon 
the stability of the powder. At temperatures below, say, 6o° F., 
the stability is not appreciably affected. At temperatures above 
yo° F. the rate of decomposition rises quickly with rises in tem¬ 
perature, becoming - high at 90° F. and dangerously accelerated at 
temperatures over ioo° F. Precautions are therefore taken to 
insure the maintenance of a uniformly low temperature as far as 
possible in the magazines in which powder is kept on shipboard 
and elsewhere. 

Since the presence of moisture favors decomposition, the con¬ 
tainers in which the powder is stowed are made airtight and every 
effort is taken, through care in handling, to maintain their tight¬ 
ness. A leaky container may not only admit undesirable moist 
air to the powder, but may permit the loss of volatiles through 
evaporation, especially if the air in the container is changed 
through alternate expansion and contraction due to changes in 
temperature. 

The Navy Regulations prescribe a rigid series of periodical 
tests whereby the stability of each index of powder on board ship 
or elsewhere may be observed, and also require the strict exercise 
of the precautions necessary to insure the longest possible main¬ 
tenance of a stable condition. Under normal conditions of storage 
any possible decomposition is very slow and the tests prescribed 
will give unmistakable evidence of decomposition long before such 
decomposition becomes dangerously advanced. This fact must, 
however, not influence anyone charged with the care of powder to 
relax in any degree the vigilance with which the powder is 
observed and safeguarded from unfavorable conditions. 

47 . Loss of volatiles.—Loss of volatiles, through leakv con- 
tainers or otherwise, will increase the rate of combustion of the 
powder; hence it will increase the pressure in the gun due to a 
given weight of charge. It is possible that a charge which has 
lost volatiles to a considerable extent may produce dangerously 
high pressure when fired. Such powder has sometimes been said 
to be dynamically dangerous. “ Ballistically dangerous ” would 
probably be a more descriptive term. It is readily seen that the 
same precautions—tight containers and uniformly low tempera- 


Service Explosives 


47 


tures—which guard against the development of “ unstable or 
chemically dangerous” powders will also guard against the de¬ 
velopment of ballistically dangerous powders. Under normal 
conditions of storage powders will not lose volatiles to any 
appreciable degree. 

A powder which may have become dangerous chemically 
through partial decomposition is not dangerous ballistically since 
a part of the decomposition, which should take place in the gun 
with sudden evolution of heated gases, has already taken place 
and the powder has lost a corresponding number of heat units. 

(2) GUNCOTTON. 

48 . (a) Properties.—Guncotton is composed of nitrocelluloses 
of higher degrees of nitration than those which are used for 
smokeless powders. The nitration of military guncottons is over 
12.9 per cent. Guncotton is very much like ordinary white cotton 
when pure. When wet it retains its chemical stability for long 
periods during storage and is quite insensitive to flame, shock, or 
friction. It can, however, be detonated, even when wet, by means 
of a proper detonator and booster. The means usually used for 
initiating detonation in wet guncotton are a fulminate detonator 
acting through a booster or “ primer ” of TNT or dry guncotton. 

Dry guncotton is a powerful explosive and is much more sensi¬ 
tive than wet guncotton. It requires special care in storage for 
this reason and for the reason that it is not as stable chemically 
as wet guncotton. 

(b) Uses.—Wet guncotton was for many years the principal 
explosive used in various military services for torpedoes, mines, 
and demolition charges. It was used for these purposes in the 
United States Navy for a long period, but is no longer being 
manufactured for such use, since the adoption of TNT. 

Dry guncotton is used as a primer for wet guncotton charges; 
and as one of the components in certain types of detonators and 
cannon primers, solely as a flame producer to be ignited from an 
electric bridge wire. 

(c) Manufacture.—The manufacture of guncotton is similar 
to the manufacture of nitrocellulose for smokeless powder, except 
that the nitrating process is more sustained in order to produce a 
higher percentage of nitration and differs somewhat in other 


48 


Naval Ordnance 


details. The nitrated cotton passes through a purification process 
consisting of washing, preliminary boiling, pulping, and poaching 
similar to the process used in the purification of nitrocellulose for 
powder. After purification the guncotton is usually pressed into 
blocks of the desired form. Wet guncotton contains water in the 
amount of about 25 per cent of.the dry weight of the guncotton. 
This percentage is maintained during storage by the addition of 
distilled water from time to time as required. 

(3) BLACK POWDER. 

49 . (a) Properties.—The composition of black powder varies 
somewhat, depending upon the use for what it is intended. The 
usual composition, however, is about as follows: Saltpeter 
(potassium nitrate), 75 per cent; charcoal, 15 per cent; sulphur, 
10 per cent. The form of the powder also differs, depending upon 
the use for which it is intended. When made up in grains, the 
powder has a somewhat glazed surface and is free from dust. 
For certain special purposes, for instance in fuses, a very fine 
black powder known as fuse powder or meal powder is used. 

(b) Manufacture.—The ingredients are powdered by grinding 
separately before mixing. A preliminary mixing is then given, 
usually in a rotating wooden drum containing lignum vitae balls. 
The mixture is usually thoroughly incorporated in a mill in which 
the mixture is ground and worked under large slow-moving 
rollers. In this process the mixture cakes somewhat and it is 
therefore broken by hand before passing to the press. In the 
press the powder mixture is subjected to high pressure to produce 
a dense, hard mass. The pressed mass is broken up and passed 
through a granulating mill where it is broken into smaller grains 
by passing through several pairs of rolls. These grains are 
separated into different sizes by passing through sieves. The 
grains are glazed by being tumbled about in rotating wooden 
drums. Some powders, especially larger grain sizes, have graphite 
added to facilitate glazing. After glazing the powder is usually 
dried under moderate temperatures. 

(c) Uses.—Black powder is used in the United States Navy 
for (1) ignition charges, both in pads sewed into the bags con¬ 
taining smokeless powder, and in brass cannon primers; (2) in 
powder trains for fuses and similar devices, where the powder is 


Service Explosives 


49 


loose if intended for instantaneous transmission of flame, and 
pressed hard if intended for a delay or time train; (3) as the 
bursting charge in several classes of projectiles, such as common 
projectiles, shrapnel, and star shell, where extreme disruptive 
force is not needed or where the bursting charge is intended only 
to open the shell and discharge its contents ; (4) for blank charges 
in saluting guns; (5) for torpedo impulse charges. 

(4) TRINITROTOLUENE (TNT). 

50 . (a) Properties.—Trinitrotoluene, frequently called trini¬ 
trotoluol, or TNT, is a crystalline solid of the formula C 0 H 2 
(N 0 2 ) 3 CH 3 . When pure it has a pale yellow color and a melt¬ 
ing point of about 80.5° C. When exposed to light its color 
becomes darker, approaching a dark red, and its melting point is 
somewhat lowered. Two grades of TNT are used in the United 
States Navy, one of high melting point which is called “ Grade A” 
or “ refined ” TNT, and one of lower melting point which is 
termed “ Grade B ” or “ crude ” TNT. The other principal 
physical differences in these two grades are that Grade A TNT 
has lighter color, better crystalline form and is freer running. 
Grade B TNT has about the color and consistency of brown sugar 
and it tends to agglomerate or pack. Both grades can readily be 
melted and poured into containers to solidify. When TNT is 
cast its color changes to a deep yellow brown. TNT may also be 
run into cold water from the molten state. It will then assume 
the form of pellets. 

TNT is nearly insoluble in water. It is practically non-hygro- 
scopic and absorbs moisture only to a negligible degree when 
exposed to damp atmosphere. A cast charge of TNT is im¬ 
pervious to water if its surface is unbroken. TNT in any form 
may remain under water or exposed to water for long periods 
without harmful effect, and, when dried out, should be as efficient 
as before. Water present with granular TNT will, however, 
affect the readiness and completeness with which it is detonated. 
When the amount of water reaches about 15 per cent by weight, 
the granular TNT cannot be detonated with the detonators usually 
used. 

TNT is neutral in its reaction and does not form sensitive 
compounds by reaction upon metals, as does picric acid. It is 


5 


50 


Naval Ordnance 


chemically stable and will retain its stability for long periods even 
under variable and unfavorable conditions of storage. In fact, 
its stability life seems almost unlimited. 

TNT is quite insensitive to impact, friction, and pressure. 
When it is ignited in the open it burns slowly, giving off a dense, 
black smoke. If ignited confined, the rate of combustion increases 
and explosive effects result. TNT can be detonated only by the 
application of a powerful shock from another explosive detonated 
in contact with it or in close proximity to it. The safety with 
which TNT can be handled and transported has recommended 
it highly for various military uses. Like all explosives, it must 
however be treated at all times with every reasonable precaution. 

“ Grade A” TNT is detonated more readily than “Grade B ” 
TNT, and granular or pelleted TNT is much easier to detonate 
than the cast form. A granular or pelleted booster charge of 
“ Grade A ” TNT is therefore usually used in detonating charges 
of cast TNT. 

The disruptive force of TNT has been stated as roughly io per 
cent less than that of picric acid, and slightly greater than that of 
wet guncotton. When detonation is complete it gives off a con¬ 
siderable volume of black smoke, due to the uncombined carbon 
resulting from the reaction. When detonation is incomplete the 
smoke given off is yellow or yellow gray due to the presence of 
unconsumed TNT. The rate of detonation of TNT is about 7000 
meters per second. 

Unless very pure, TNT usually contains a certain proportion 
of isomers (that is, substances having the same chemical formula 
but with a different molecular arrangement). These isomers have 
a lower melting point than the pure TNT and they therefore tend 
to segregate and exude, especially from “ crude ” TNT, and more 
particularly from cast charges. This exudation increases with 
increased temperature. The appearance of these isomers, exuding 
from TNT containers as dark brown oily liquids, is not uncom¬ 
mon and need not cause alarm. The isomers are detonated less 
readily than pure TNT and their presence therefore affects the 
readiness with which the whole charge is detonated, but it appears 
that they take part in the reaction when the whole charge deto¬ 
nates. The isomers are inflammable to about the same extent as 
TNT and are not more sensitive to impact or friction. Their 
presence does not appear to affect chemical stability. 


Service Explosives 


5i 


(b) Manufacture.—Trinitrotoluene is produced by the nitra¬ 
tion of toluene, C 0 H 5 (CH 3 ). This substance is one of the oily 
liquids present in coal tar and separated from it by fractional 
distillation. 

The nitration is carried out by treating toluene with a mixture 
of nitric and sulphuric acids at a temperature of about 160° F. 
The reaction proceeds in steps, the initial product being mono- 
nitrotoluene, which by further nitration is converted to dinitro- 
toluene, and finally to trinitrotoluene. The progressive nitration 
is sometimes carried out in a single container or kettle, the suc¬ 
cessive steps being brought about by the addition of fresh acids 
to strengthen or fortify the mixture; it is sometimes carried out 
by conducting the three steps in three sets of nitrators, the third 
step requiring the strongest acids. 

After the spent acid from the last step in the nitration has been 
drained ofif the crude trinitrotoluene is crystallized by melting in 
strong sulphuric acid and cooling. The acid carries ofif impurities 
in solution and the trinitrotoluene crystallizes out in cooling. The 
crude trinitrotoluene is washed several times with hot water until 
the remaining acids are removed. It is then melted in a steam- 
jacketed pan and heated until the water is driven ofif, and recrys¬ 
tallized by cooling while being stirred constantly. 

Purification and recrystallization is often carried out by treating 
with various solvents other than sulphuric acid, such as alcohol, 
alcohol and carbon tetrachloride, and sodium sulphite solution. 
The methods used dififer with various manufacturers. 

During the manufacture of trinitrotoluene and its subsequent 
handling workers are often subject to a slow poisoning through 
inhalation of vapors and dust, or absorption of material through 
the skin. The efifect of this poisoning usually wears ofif when 
exposure is stopped and can be prevented or much reduced by the 
wearing of gloves and protective clothing, and by washing the 
clothing and body carefully. 

(c) Uses.—Trinitrotoluene is used in the United States Navy 
as the main charge in the later types of mines and torpedoes, in 
depth charges and in aero-bombs. For these purposes “ Grade 
B ” trinitrotoluene is used. It is cast into the explosive chamber 
and in this state has a density of about 1.5. 

“Grade A” trinitrotoluene is used in crystalline form with a 
density of about 1.0 for primer or booster charges in the weapons 


52 


Naval Ordnance 


named above. The weight of the booster charge is usually about 
1.5 to 2.0 per cent of the weight of the main charge. Crystalline 
“ Grade A ” trinitrotoluene has also been used for booster charges 
in certain types of fuses. 

Various high-explosive projectiles not intended for use against 
armor have been loaded with trinitrotoluene bursting charges. 
“ Grade A ” trinitrotoluene has been used for this purpose, in some 
cases in compressed crystalline form, in other cases cast. 

(5) TRINITROXYLENE (TNX). 

51 . Trinitroxylene, or TNX, C G H(N 0 2 ) a (C H 3 ) 2> is produced 
by the nitration of xylene, C 6 H 4 (CH 3 ) 2 , which like toluene is 
obtained from coal tar. This substance is a brown crystalline 
solid, whose physical and chemical characteristics are analogous 
to those of TNT, and whose stability and safety are comparable to 
those of the latter. It is detonated with more difficulty than 
TNT, but in mixture with the latter in proper proportions gives 
an explosive substance which is practically as satisfactory for 
cast charges. 

The use of this mixture, sometimes called toxyl, was developed 
for and under the Bureau of Ordnance during the World War, 
in order to conserve the supply of TNT. 

(6) PICRIC ACID. 

52 . Trinitrophenol or picric acid, C„H 2 (NO.)., • OH is derived 
from phenol, C 6 H 5 • OH, otherwise known as carbolic acid. It is 
a yellow crystalline solid of good chemical stability and highly 
explosive properties when properly detonated. It has good 
chemical stability except that it is prone to act upon metals to form 
metallic picrates which are very sensitive explosive substances. 

(a) Manufacture.—Picric acid manufacture is usually carried 
out in two stages. In the first stage phenol is treated with sul¬ 
phuric acid. This sulphonation results in the production of 
phenolsulphonic acid, which is nitrated with nitric acid to form 
trinitrophenol. The product is carefully purified by washing with 
water. 

(b) Uses.—Picric acid has been used as a booster material in 
various'types of fuses and has been employed by various countries 
as a bursting charge for projectiles. Ammonium picrate, 


Service Explosives 


53 


\ 


C 6 H,(NO,) 3 ONH 4 , has been preferred by some for the latter 
purpose, since it does not form the sensitive metallic picrates. 

(7) TETRYL. 

53 . Tetryl, or tri-nitro-phenyl-methyl-nitramine, C 6 H,(N 0 2 ) ;! 
N(CH ;j ) (NO,), a yellow crystalline explosive substance, some¬ 
times called tetra-nitro-methyl-aniline, is usually produced by the 
sulphonation and nitration of dimethylaniline, which is produced 
from aniline and methyl alcohol. The product is purified by wash¬ 
ing in water, drying and recrystallizing from hot benzol. 

Tetryl is more sensitive than TNT or picric acid and is much 
used for boosters and detonating trains in various types of 
detonating fuses. 

(8) FULMINATE OF MERCURY. 

54 . Fulminate of mercury, HgO,C,N,, is a fine yellowish-white 
crystalline explosive substance, which is highly sensitive to heat, 
impact, and friction. It is insensitive when wet and is usually 
handled wet in manufacture. It is produced by dissolving mer¬ 
cury in strong nitric acid and running the solution into alcohol. 
The product is thoroughly washed and is usually dried only 
shortly before loading. 

The sensitiveness and explosive violence of fulminate of mer¬ 
cury make it especially suitable for the initiation of explosive 
reactions in other substances. It is used in fulminate caps, usually 
mixed with potassium chlorate, antimony sulphide or other 
materials which produce a longer flame, to ignite powder charges, 
either directly, as in small arms, or through black powder ignition 
charges contained in the same primer with the cap. The use of 
further ignition charges of black powder in the powder bags of 
larger guns has already been described. 

Fulminate or fulminate mixtures are also widely used in deto¬ 
nators of all kinds to initiate the detonation of high explosives 
either directly or through boosters. 



CHAPTER III. 

ELEMENTARY INTERIOR BALLISTICS. 

Section I.—Definition and Scope. 

55 . Ballistics as a whole may be considered the study of the 
general system by which a projectile is fired from a gun to hit a 
distant target. 

Evidently the study of the system may be readily divided into 
two branches, i. e., exterior ballistics, dealing with the flight of 
the projectile after leaving the muzzle of the gun, and interior 
ballistics, with the movement of the projectile within the gun. The 
connecting link between the two branches is obviously the muzzle 
velocity of the projectile, both direct and rotational. 

56 . The artillerist demands, for the purpose of exterior bal¬ 
listics, a certain velocity. From the principles of interior ballistics, 
and the form of the gun, che weight and characteristics of the 
powder must be determined in order that such a muzzle velocity 
may be produced without undue strain on the gun. The artillerist 
naturally desires a maximum velocity for great range and flat 
trajectory; the designer must consider the strength of his gun and 
desires the minimum wear or erosion therein; the velocity finally 
agreed upon must be in the nature of a compromise between the 
two. 

57 . To determine the velocity of the projectile in the gun, with 
the accompanying pressures and action upon both projectile and 
gun, and the effect upon these pressures and velocities of changes 
in any of the “ conditions of loading,” such is the field of interior 
ballistics. By “ conditions of loading ” are meant the powder 
used, the zveight of charge, the density of loading, the volume and 
form of the powder chamber, and the weight of the projectile. 

To insure clarity in the following discussion, several elementary 
definitions must here be given : 

58 . A gun is a mechanical device, composed essentially of a 
tube, closed at one end at the moment of firing, capable of contain¬ 
ing a projectile and a propelling charge and of so controlling the 
explosion of the charge as to discharge the projectile with a high 
velocity. 


55 


56 


Naval Ordnance 


The gun must fulfil the following conditions : 

1. Mechanical conditions .—Its construction must be such as to 
withstand the action of the rapid burning of the propelling charge. 
After the stresses upon the gun have been determined by the 
processes of interior ballistics, its construction is governed by the 
study of the “ elastic strength of guns.” 

2. Ballistic conditions .—The gun must produce a given ballistic 
result, i. c., must deliver a certain weight of projectile at a given 
muzzle velocity with minimum possible stresses on the gun. 
These conditions are the special field of the study of interior 
ballistics. 


3. Service conditions .—The gun must easily fulfil the neces¬ 
sities of the service relating to the working of the breech, the 
loading, training, and aiming of the gun. The last two, however, 
are more properly matters of the gun mount rather than the gun 
itself. 

59 . The pozvder chamber is that portion of the gun wherein the 
powder is contained before the firing of the gun. Since the pro¬ 
jectile is seated at the forward end of the chamber and the gun 
is closed at the rear end by the breechblock, it may be seen that at 
the instant of firing and until the movement of the projectile, the 
powder chamber becomes the container of the powder gases. It 
may, therefore, be expected that the volume of the powder cham¬ 
ber plays an important part in the study of interior ballistics. 

The bore of the gun is that part wherein the gun is of a uniform 
diameter, from muzzle to pozvder chamber. The length of the 
bore represents the total travel of the projectile in the gun. 

60 . The “ density of loading ” is the ratio of the zveight of the 
charge to the zveight of a volume of zvater at standard tem¬ 
perature sufficient to fill the pozvder chamber. One pound of water 

occupies 27.68 cubic inches; hence, if S' is the volume of the 

c 

powder chamber, the equivalent weight of water is pounds. 

a> 


Now as w is the weight of the powder charge, ■ \ , is the density 

27.00 

of loading, expressed usually as A. Then, simplifying, we have 



(1) 





Elementary Interior Ballistics 


57 


61. Known elements.—In proceeding' to the mathematical ex¬ 
amination of the action of the gun, the following elements are 
considered for the moment known and fixed. Once their inter¬ 
relation is determined, then the effect of variation in one or more 
may be determined. \ he notation used is that generally employed 
in works on interior ballistics. 

Elements of the gun: 

u, travel of the projectile in the bore, in feet. 

A, area of the cross-section of the bore, in square inches. 

S, volume of the powder chamber, in cubic inches. 

Elements of the projectile : 

w, weight of the projectile, in pounds. (It is to be noted that 
in interior ballistics its shape and contour are of no im¬ 
portance save that it must close the bore when loaded in 
the gun.) 

Elements of the charge: 

w, weight of the charge, in pounds. 

A, density of loading. 

Unknown elements, or elements physically measured as a 
result of actual firing—used as check on calculated results: 

V, velocity, in feet per second. 

P, maximum pressure in the bore, in tons per square inch. 

62. Mathematical analysis, based upon certain fundamental 
assumptions, allows the deduction of various formulas concern¬ 
ing these elements, from which the action of the gun may be pre¬ 
dicted. Such formulas give the interrelation of the elements of 
pressure, velocity, travel of the projectile, form of chamber and 
bore, so that, when certain of these elements are known, the 
remainder may be found. 

63. The uses of these formulas may be appreciated. 

First, in the design of the gun. Given the desired muzzle 
velocity, and the limiting maximum pressure allowable in the gun 
(determined from study of gun construction); the volume of 
powder chamber and the weight of charge may be determined. 
From these the pressures existing successively in the bore as the 
projectile travels down the gun may be found, and the gun may 
then be constructed so as to afford sufficient strength throughout 
its length. 

Second, in the design of the powder. From the action, as 
regards pressures and velocities, of a powder in one type of gun. 


58 


Naval Ordnance 


the most suitable powder may be designed for a gun of similar 
proportions but of different caliber. 

Third, in the interchangeability of powder. With the results 
of firing in one gun, the action of the same powder in another 
type of gun may be predicted. 

Fourth , and generally, the resultant changes to be expected 
from variation, with a certain gun and powder, of any of the 
several elements, i. e., change of weight of powder charge, and of 
resultant pressures, necessary to produce standard muzzle velocity 
when the weight of the projectile is altered; reduction of weight 
of powder charge to produce a standard reduced velocity; and 
similar problems. 

64. The results obtained by the use of the formulas are not 
infallible, but in general are close approximations to actual results 
obtained on firing with elements calculated from the formulas. 
Calculated results are always tested by actual firing at the prov¬ 
ing ground, to insure against inaccuracy. The calculations, how¬ 
ever, provide a starting point for such tests. When information 
is desired in advance of any possible proof work; as in planning 
ammunition stowage and loading arrangements aboard new 
vessels, necessitating knowledge of weight and volume of charges; 
and, as above, in designing guns or powders, invaluable data are 
afforded by the application of interior ballistics formulas. 

In oilier words, while the results obtained from theory are not 
to be regarded as final without proof, yet the knowledge of the 
principles of interior ballistics is and has been vitally necessary to 
the development of naval ordnance. 

Section II.—Fitting the Powder to the Gun. 

65. As has been shown in the preceding chapter, smokeless 
powder, even though made of a standard nitration and uniform 
shape of grain, may be so manufactured, with different sizes of 
grain, and therefore different web thicknesses, that different 
speeds of burning may be obtained. 

66. When the powder charge in a gun burns, a large quantity 
of highly heated gases is formed. For a given weight of powder, 
die total quantity by weight of such gases is constant, and is equal 
to the weight of the powder charge, since all of the smokeless 
powder is converted into gas. Now, if the powder charge is 
entirely consumed before the projectile moves, the container for 


Elementary Interior Ballistics 


59 


these gases is evidently the powder chamber only, and the large 
quantity of the gases, confined within the chamber and at a high 
temperature, tends to produce pressures so high as to endanger the 
gun. Hence, if all of the charge is consumed before motion of 
the projectile begins, but a small charge may be used with safety 
and the total amount of gases, or the total energy of the powder 
charge, must be correspondingly low. 

If, however, the projectile commences to move after but a por¬ 
tion of the powder charge has been consumed, the space for ex¬ 
pansion of the powder gases becomes greater and a larger quantity 
of gas may be contained without undue stress on the gun. Hence, 
a large powder charge may be employed and the total energy of 
the propelling charge for the gun may be increased. As the pro¬ 
jectile moves, the powder is consumed, and is eventually all burned, 
while the projectile is in the gun, but not, as in the first instance, 
before the projectile has moved from its seat. 

It is necessary, then, to use a powder of such speed of burning 
that the projectile has left its seat and moved forward before the 
powder is all consumed. It must be noted, however, that the 
speed of burning must not be so slow that any part of the powder 
is unconsumed when the projectile has left the gun, for obviously 
such remaining portion is wasted, as its gases, formed after the 
projectile is expelled, can exert very little if any efifect upon the 
latter. 

67. The time of burning of a powder, under a given standard 
pressure, is dependent upon its nitration, its remaining volatiles, 
the shape of the grain, and the web thickness—the latter, in a 
standard geometrical form of grain, dependent upon the size of 
the grain. Our practice is to keep nitration and shape of grain 
uniform, to restrict the remaining volatiles within narrow limits, 
defined by the size of the grain, since it is more difficult to drive 
out the volatiles from the larger grains, and to obtain the variation 
in speed of burning by using different sizes of grains. 

(Note. —In very small powder grains, owing to difficulty of manufacture, 
the standard multi-perforated grain is not used, a single-perforated cylin¬ 
drical grain being employed.) 

68. The various types of guns, with different diameters of bore 
and lengths in calibers, each with its own muzzle velocity, which 
may or may not be the same as that of other guns, present different 
requirements for the powder. The lengths of travel of the pro- 


6o 


Naval Ordnance 


jectile, and consequently the times of its travel, differ largely. 
Prom this fact alone, it is seen that different powders must be 
used for the several types of guns. In addition, the volume of the 
powder chamber and the weight of the projectile introduce ele¬ 
ments which must, as will be seen later, enter into the selection 
of a powder for a gun. 

69. The powder must be fitted to the gun, i. e., the proper or 
most suitable size of grain must be found, in order that we may 
have the desiderata noted above, a charge only partly consumed 
when the projectile starts to move, so that no dangerous pressures 
may be caused, and yet wholly consumed before the projectile 
leaves the muzzle, in order that the total energy of the powder 
may be utilized. These general ideas will be delimited more 
clearly later, but with this conception of the necessity of selecting 
the powder for the gun the analysis of the development of the 
pressure inside the gun may now be considered. 

70. First consider the simplest case, an instantaneous combus¬ 
tion with an “adiabatic expansion.” An "adiabatic expansion” 
is that in which the gas expands and performs work in a space 
impermeable to heat. That is, the gas neither receives nor loses 
heat from or to its container, although in performing work it of 
course gives up its energy, in the form of heat; thus its tempera¬ 
ture, and, since it is expanding, its pressure, both diminish. 

By Charles’ law, 



( 2 ) 


Or, the product of the pressure times the volume of a gas varies 
directly as the absolute temperature (measured from absolute 
zero, — 273 0 C.) of the gas. This may be expressed bv putting 


PV = RT (see Art. 19 ), 


(3) 


that is, the pressure times the volume of the gas is equal to a 
constant times the absolute temperature of that gas. This is the 
fundamental equation of the gaseous state. Let F = RT, and con¬ 
sider the gas of unit weight confined in unit volume. Then P—F, 
and F is the pressure per unit surface from unit weight of gas in 
unit volume. When R is a constant properly computed for the 
gases from gun powder, then F becomes a factor dependent upon 
the temperature. For a given chemical composition of powder so 
employed in guns as to obtain a standard maximum pressure on 
firing, F is nearly constant and may be evaluated by experiment. 


Elementary Interior Ballistics 


6i 


71. The fundamental equation quoted above has been found, 
on critical analysis by thermodynamics, to be only approximate, 
and the true equation becomes (using Clausius’ form of the 
Vander Waal formula for gases and vapors), 


p= RT_ _ C{V-a) 
~V-a T{V + /3A 


The second term disappears for high temperatures, as C is a 
diminishing function of T, the formula then becoming (see Art. 
20 ) 


RT_ 

V-a' 


( 4 ) 


This equation is for unit weight of power. If the volume V is 
unchanged, as the volume of the powder chamber of a gun, and 
the weight of powder charge is changed the equation for unit 
weight then becomes 



to 

A 


— aw 


Putting RT — F, and simplifying, 


P- 


F A 

I -aA * 


(5) 


which expresses the relation between tbe density of loading and 
the pressure of the gases in instantaneous combustion. (See Art. 
20 .) 

72. The curve of pressure within the gun, using pressures as 
ordinates and travels of the projectile as abscissas, is therefore 
plotted as in Fig. i. The initial pressure is given by the above 
equation, and the curve takes the form BM , the standard adiabatic 
curve of thermodynamics. The area of the curve, from the ordi¬ 
nate AB, represents the energy stored in the projectile, or the 
work done upon the projectile, at every point of the travel. 

With these hypotheses, it is possible to compute these areas and 
to obtain approximate formulas giving the velocity of the pro¬ 
jectile in the gun and the corresponding pressure. 

73. Such for an instantaneous powder. However, it has been 
seen that a powder not instantaneous, but one which affords a 
progressive combustion, must be employed. 




62 


Naval Ordnance 






Fig. 2. 











Elementary Interior Ballistics 


63 


For such a powder ( 1 . e., progressive), the pressure will start 
from zero and will rise at first very quickly, on account of the 
production of gases, but soon the motion of the projectile, in¬ 
creasing the capacity of the powder chamber, will have the effect 
of reducing the pressure. For a while the increase of pressure 
due to the combustion of the powder will be greater than the 
reduction due to the motion of the projectile, and the pressure 
will continue to rise; but soon a time will come when both causes 
will be equal, and that will give the maximum pressure M. After 
that, the production of gas will not be sufficient to compensate for 
the increase in volume, the pressure will decrease, and when the 
powder is completely burned the curve will take the adiabatic 
form. 

The curve of progressive powder AM is shown in full line; 
that of the instantaneous combustion by dotted line (Fig. 2 ). 

74. The charges and the potential (or heat units) of the pow¬ 
ders being the same, the curves, when indefinitely produced, will 
have the same area, and this is why at a certain point the curve 
of progressive powder runs higher than the other. If C is the 
muzzle of the gun, we see that the lost energy is greater with the 
progressive combustion, and consequently the efficiency of the 
powder is smaller. 

Assuming that the powder to which curve AM corresponds 
belongs to a category whose combustion is still relatively quick, 
we see that the passage of the powder from instantaneous to 
progressive combustion results in a drop of the maximum pressure 
from B to M. 

Should we pass, now, to a combustion still slower, with a charge 
of the same weight and a powder of the same composition, the 
maximum pressure will fall from M to M ', but as the area of 
curve AM, infinitely expanded, equals the area of AM', also 
infinitely expanded, at a certain point AM' will rise above AM and 
more loss is indicated at C, which proves that the efficiency of the 
slow powder is less than that of the quicker powder. In very slow 
powders the grains are not entirely consumed and a greater loss 
of efficiency results. 

Since the use of a slower powder allows the lowering of the 
maximum pressure, with a reduction, it is true, of the initial 
velocity, one is led, naturally, to inquire if, in increasing the 
charge of a slower powder in such a way as to keep the same 


64 


Naval Ordnance 


maximum pressure as that of the quicker powder, it is not possible 
to obtain more velocity than with the quicker powder. 

This is effectively what happens. 1 he curve of pressure takes 
the direction AM", and there is a notable increase of the initial 
velocity in the same gun, for the average or mean pressure down 
the bore is greater. 

It is possible, then, by using larger and larger charges of 
powders slower and slower, between certain limits at least, to 
obtain more and more velocity without going beyond the maxi¬ 
mum pressure permissible in the gun. But the efficiency of the 



Fig. 3. 

powder will be less and less, as shown by the lost pressure at the 
muzzle, this loss being measured by the height of the ordinate 
above the point C. To get more work from the powder the gun 
should be lengthened as much as the service conditions permit. 

75. It will not be advantageous, then, to fire a slow powder in a 
gun not previously built for it. Besides, the regularity in the 
initial velocity of a gun is closely connected with the efficiency of 
the powder. The greater the efficiency the greater the regularity. 
When the efficiency is so low that unburned powder remains, con¬ 
siderable irregularity may result. 

It will be noted that with the slower powders the point of maxi¬ 
mum pressure moves toward the muzzle of the gun, and the 







Elementary Interior Ballistics 65 

pressures throughout the subsequent travel of the projectile are 
higher, thus necessitating stronger construction for the chase 
of the gun. 

76. The mean pressure is an imaginary constant pressure, 
which, acting upon the base of the projectile during its travel in 
the bore, would give the projectile an initial velocity equal to that 
actually obtained by the pressure acting as above described, or, in 
other words, would, when drawn on the curve, produce a work 
area equal to that of the curve of actual pressures. This follows, 
since for equal muzzle velocities, representing equal energies de- 



Fig. 4. 

livered at the muzzle, the work areas must necessarily be equal. 
With the mean pressure a good idea can be had of the work 
performed by the powder in the gun by comparing the mean to the 
maximum pressure. 

Assuming (Fig. 3 ) a quick powder, whose curve takes the shape 
OMA, the mean pressure will be drawn in such a way that the 

OF 

area EMB = BDA, neglecting OFF; the expression ^ repre¬ 
sents the ratio of the mean pressure to the maximum pressure. 
Assuming (Fig. 4 ), on the other hand, a slow powder, whose 

. OF 

pressure curve takes a more flattened shape, OMA, the ratio 


6 








66 


Naval Ordnance 


of the mean to the maximum pressure will be greater than the 
preceding one. It results from this that the ratio of the mean to 
the maximum pressure will give, by comparison, some informa¬ 
tion about the qualities of the powder used. 

The mean pressure can easily be computed from the relation 


%mV 2 =P e xAxu 

p _ wV 2 


( 6 ) 



in which 



V represents the initial velocity, in feet per second. 

A represents the cross-section of the bore, in square inches. 
u represents the travel of the projectile in the bore, in feet. 

P e represents the mean pressure, in pounds per square inch. 

77. This gives now a clear understanding of the meaning of 
quick and slow powder. A scale of relative quickness can also be 
established, starting from the quickest, the powder of instan- 

OF ■ ■ • 

taneous combustion, in which -qjj 1S a minimum, and proceeding 

to the imaginary powder in which the maximum pressure is con¬ 
stant and, consequently, equal to the mean pressure. The ratio 
O F 

is also a factor for the selection of the powder most suitable 

ON 1 

for a gun in function of its elastic strength, because the slower 

the powder the greater the stress at the muzzle. In the naval guns 

0 F 

the ratio varies from 0.47 to 0 . 7704 . 

78. To quote from a French authority : * 

“ These considerations explain the experimental results obtained 
when, in a given gun, increasing charges of slower powders are 
fired, maintaining such weights of charges as to keep a constant 
maximum pressure. The muzzle velocities increase at first until 
the successive increases become very small in proportion to the 
added weight of charge. The powder finally arrived at is ‘ the 
maximum powder,’ at the given pressure, for the weight of pro¬ 
jectile used. 

* Maxime Cremieux, engineer in chief of naval artillery, “ Naval Powders: 
Applied Interior Ballistics, 1914.” 







Elementary Interior Ballistics 


6 7 


“ The small final gains of velocity are due to the fact that the 
powder is not completely burned in the gun, which is too short in 
proportion to the slowness of the powder. 

“ Because of this small gain, the use of the maximum powder is 
not advantageous. It is all the less so. since the velocity tends to 
become irregular, the amount of powder not completely burned 
varying from one shot to another. 

“If there are fired, at the constant maximum pressure, powders 
slower than this maximum powder, the velocities decrease, the 
fraction of powder unburned increasing. Grains of powder in¬ 
completely burned may be thrown from the muzzle of the gun. 
The irregularity of the velocity increases, and is shown by high 
variation of successive velocities from the mean. At the same 
time, and especially in the case of powders of irregular grain- 
shape', pressure gauges show irregular pressures, due to ‘ waves ’ 
of pressure. 

“ The problem of the determination of the most advantageous 
condition of loading consists in obtaining, with a given maximum 
pressure and weight of projectile, the maximum muzzle velocity 
compatible with a satisfactory regularity, indispensable to proper 
control of fire. The powder to employ is therefore that which 
immediately precedes ‘ the maximum powder.’ ” 

79. In this analysis two important points have, for the sake of 
simplicity, been omitted. 

In constructing the pressure curves, the curve has, in all save 
the curve for instantaneous combustion, been drawn through the 
origin, assuming zero pressure for zero travel of projectile and a 
small pressure for a minute travel thereof. In practice, however, 
the pressure must rise above the “pressure of forcing” before the 
projectile begins to move. This pressure of forcing is caused by 
the inertia of the projectile partly, but mainly by the resistance 
offered to its passage by the rifling band before it has been forced 
through the origin of rifling. This necessary pressure is from 
3 to 5 tons per square inch. 

80. The curve of pressures and its resultant work area repre¬ 
sents only the work done on the projectile. The total energy of 
the powder, equivalent to weight times chemical potential heat 
energy per pound, is employed in (i) work upon the projectile 
as shown by the curve, ( 2 ) heating the projectile and the walls 


68 


Naval Ordnance 


of the chamber and bore, ( 3 ) minutely expanding the gun, ( 4 ) 
internal work in expanding the gases, ( 5 ) the recoil of the gun 
and other minor losses, such as rotation of projectile, forcing, 
friction, etc. Ingalls (revised 1911 ) states that 83 per cent of the 
energy of the powder is expended upon the motion of the pro¬ 
jectile. Since the work is shown by the work area on the curve, 
we may expect that the pressure curve for all work done, and 
therefore for the actual pressure in the gun, should run higher 
than that drawn for the work done on the projectile alone. This 
is found to be the case, since the actual pressures as measured by 
gauges are 12 to 15 per cent higher than the curve. 

81. To make use of the foregoing, it is necessary that formulas 
should be available to compute the approximate pressure curve 
of the powder. Based on the preceding fundamental principles, 
there have been deduced experimentally and mathematically semi- 
empirical ballistic formulas. The object of these is to determine 
the pressure of the gases at any point of the travel of the pro¬ 
jectile, and the velocity thereof at that point. 

Section III.—Historical. 

82. Rodman’s experiments and analyses, unfortunately cut 
short by the needs of the service at the beginning of the Civil 
War, were followed up more thoroughly in France than in the 
United States. With few exceptions, the French artillerists have 
conducted the most exhaustive researches into interior ballistics. 

Emile Sarrau, engineer in chief of the French powder factories, 
was the first to derive, by exhaustive mathematical and experi¬ 
mental researches, formulas for the action in the gun of geo¬ 
metrically grained black powders. He considered the elements 
of granulation, density, and velocity of combustion of the grain—• 
both in air and in the gun—and obtained working formulas which 
gave results confirmed almost exactly by experimental firings. 
Certain assumptions, necessarily not absolutely exact, were made 
to provide an initial point for mathematical analysis, and the con¬ 
stants employed in his formulas were so modified, after experi¬ 
mental firing, as to obviate the effect of these inexact assumptions. 
These assumptions were: ( 1 ) The gases expand adiabatically; 
this, of course, neglects heat expended in heating the walls of the 
chamber and bore of the gun; ( 2 ) the time required for the com- 


Elementary Interior Ballistics 69 

plete inflammation of the charge is negligible as compared with 
the time of combustion. 

Sarrau’s formulas give expressions for the velocity and the 
pressure at any point of the travel of the projectile. They have 
been since accepted with slight modifications by all ballisticians 
as standard for black powder. At the time these researches were 
published in 1870 smokeless powder was, of course, undeveloped. 

With the development and adoption of smokeless pow'ders, it 
became apparent that the Sarrau formulas were not sufficiently 
accurate; in other words, did not fit the newer powders. This is 
not strange, when the great increase of time of combustion pos¬ 
sible with smokeless powder is considered. With such an increase 
of time larger powder 'charges became practicable (without pres¬ 
sures unduly great), producing greater density of loading, more 
powder gases, greater energy, and higher muzzle velocity. By 
reason of such changes, the formulas of Sarrau, no longer accu¬ 
rate, have been to a large degree superseded, for smokeless powder 
use, by those of more recent investigators. 

Among these may be mentioned Gossot, Liouville, Cremieux, 
Charbonnier, and Le Due of France, Glennon and Ingalls of the 
United States, and Brynk of Russia. In general, the effort of 
these- investigators, with the exception of Le Due, has been so to 
modify the Sarrau analysis and resultant formulas as to render 
them applicable to smokeless powder. 

The Le Due formulas, originally derived from the results of 
experiments for calculation of recoil pressures, have given very 
satisfactory results at the Naval Proving Ground and have been 
adopted, by reason of their simplicity and accuracy, as the stand¬ 
ard for naval use. These formulas are semiempirical, i. e., partly 
derived from theory and partly from results of firing experiments. 

The derivation and use of these Le Due expressions are given 
in the following sections of this chapter. In passing, however, it 
is of interest to state briefly the Sarrau formula for velocity. 
With constants determined by G. W. Patterson at the Naval Prov¬ 
ing Ground from the results of actual firing it is, in working form, 

V=A«AD(i — BF). 

A and B are constants determined from firing, and plotted on the 
curves shown in Fig. 5 . 


Naval Ordnance 


70 


































Elementary Interior Ballistics 


7 1 


w is the weight of powder charge. 

111% 


D — 


w*S%C» 


P — (WU)-? 

C ’ 


in which u is the travel of the projectile in the bore in feet. 
w is the weight of the projectile in pounds. 

6 " the capacity of the powder chamber in cubic inches. 

C is the caliber of the gun in feet. 

This formula gives accurate results in predicting smokeless pow¬ 
der charges for new types of guns or for new velocities in known 
guns. 

The Sarrau formula for pressure is not considered adaptable or 
convenient for use with smokeless powders and will not be quoted. 

For rough ballistic work the following relations are convenient 
and approximate: 

(a) For mechanical powders V=Aw f. 

(b) For chemical or smokeless powders V = Aw™. 

The most complete treatise on the Sarrau formulas is found in 
“ Researches on the Effects of Powder,” by M. E. Sarrau, Pro¬ 
ceedings of the United States Naval Institute, Volume X, No. i. 


Section IV.—Velocity and Pressure Formulas. 

83. The point in work with velocities and pressures which is of 
most practical importance in firing the guns is the determination 
of the maximum pressure at any point in the bore, while for the 
design of new ordnance it is very important that the formulas 
should include practically all the elements of the gun in such form 
that, with some of them given, the rest may be determined. The 
Le Due ballistic formulas have been found not only to give the 
best results, as finally adapted to our powder, but to be much the 
simplest to work with. These formulas and their derivation are 
given in the succeeding paragraphs. 

84. The following symbols are used and are concentrated here 
for reference: 

w, pounds weight of smokeless powder in the charge. 

w, pounds weight of projectile. 

A, density of loading, which varies between .4 and . 7 . 




72 


Naval Ordnance 


S, cubic inches capacity of powder chamber. 

a powder constant, dependent on form and dimensions of 
grain, amount of volatiles, and temperature of powder. 
Largest for “ slow ” powders. 

v, foot-seconds velocity at any point in the bore. 

V, foot-seconds muzzle velocity. Also written I. V. 

u, feet, travel of projectile in the bore to any point. 

U, feet, total travel of projectile in bore from origin of rifling 
to muzzle. 

A, square inches, cross-section of the bore. 

g, foot-seconds, acceleration of gravity: 32.155 at Indian 
Head, Md. 

8 , specific gravity of the powder. This varies between 1.54 
and 1.62. 

P, tons per square inch. Pressure on the base of the pro¬ 
jectile at any point. 

P r , tons per square inch, mean effective pressure on base of 
projectile during entire travel through the bore. 

P ( max )> tons per square inch. Maximum pressure on base of 
projectile producing velocity. 

P(max){.gauge tons per square inch. Maximum pressure in the 
bore, or maximum pressure gun must withstand. 

(7,1 constants depending on the powder, the gun, and density 

b,j of loading. 

85 . In the development of the formulas, it was first assumed 
that the space velocity curve of the projectile in the bore is an 
hyperbola which is expressed by the equation 


an 

~b + u ’ 



86. Dividing both numerator and denominator of the right- 
hand member of (7) by it, we have 


an 

u 


b -(- u b 


u 


u 


+1 


If, now, u be infinite, we have 

V=a. 





Elementary Interior Ballistics 


73 


That is, a is the value of when u is infinite; or, in other words, it 
is the velocity the projectile would attain in a gun of infinite 
length, when the muzzle energy would represent all the work the 
powder charge was capable of doing, there being no energy lost 
or unexpended at the muzzle. 

87 . The useful work done by a unit quantity will be equal to 
the kinetic energy of the projectile as it leaves the muzzle at some 
velocity, v, i. c. } work done equals 


If the gun be infinitely long, then as we found above, v = a, and 
this value, a, may he substituted for v in the expression for the 

kinetic energy of the projectile, and the expression will he ° , 

and this is the measure of the total useful energy contained in unit 
weight of powder expanded to infinity. This multiplied by the 
weight of the charge of powder must be equal to the total energy 
of the projectile. Now let 

p = pressure of unit weight of gas, 
v — volume of unit weight of gas, 

n = ratio of the specific heat at constant pressure to that at 
constant volume, 


then we know, from Physics, /> • v n = k (constant). 
The work done in expanding from v x io v., is 


pdi 


Hence Work 
Then if v. 2 — ce 

Work' 


V 2 (•»•„ fi> 2 k 

= ^^=*^- 55 -= — 


•7i n -1 


71 n-1 


= _JL_ x -U-. 

n — i 


v "- 1 


We designate the work done by i pound of gas in expanding 
from the volume v lr which it occupies at unit density, to infinity 
by E. Also the volume at unit density = 27.68 cubic inches (t. e., 
the volume of 1 pound of water). Substituting this value of v x 
in the expression above, we have 



1 

( 2 ^ 68 )^* 









74 


Naval Ordnance 


88. If the expansion is from any other density than unity, say 
A, to infinity, then v x — and the work done will be 


h A ' 1-1 

Work = — X 


n — i 


But 


(27.68 ) n 1 ’ 


(a) 


E = 


x 


w — 1 1 (27.68 ) w_1 ’ 

Hence (a) becomes ZTA n_1 , which expresses the work done by unit 
weight of gas in expanding from some density, A, other than 
unity, to infinity. 

This work, multiplied by the weight of the charge, w, must 


equal the energy of the projectile, , 

or 

w ' a ~ =wX£A"- 1 , 
2g 

whence 

a 2 = 2g£-°k A n ~ 

* IV 


a = V 2 gE 


w \ l 2 =! 

w A 2 • 


(b) 


89 . Using the value of E found by experiment, the expression 
V 2 gE reduces to the value 9706. But owing to losses through 
heating and expanding the gun, forcing pressure, friction, etc., 
our results will not check with the results of actual firings if we 
use this value. From long series of firings and tests we find the 
value of V 2 gE for our work must be taken as 6823. This gives 
us an empirical value of a much less than the theoretical, but by 
using this value the calculated and actual results check very 

closely. The value of-is found to be 1/12. 

Substituting these values in equation (b), we get 

0 = 6823 (S) (8) 

90 . The constant b is titmice the travel of the projectile to the 
point of maximum pressure. Hence it depends first of all, as 
between different powders, on their relative quickness, or, with 











Elementary Interior Ballistics 


75 


any particular powder, upon the form and dimensions of the 
grain, i. e., is proportional to ( 3 . It is also proportional to the initial 
air space. It is inversely proportional to some power of the 
chamber volume, and some power of the weight of the projectile, 
since increase in either of these decreases the distance to the point 
of maximum pressure. Given 

S — chamber volume. 

8 = density of powder. 

A = density of loading. 
w — weight of projectile. 

= powder constant. 

Then, according to the logic of our relative proportions above, 


j y _o initi al air space 
~ ^ S s X zv v 


(c) 


6'A 


Now —s— = space occupied by a charge of density 8 loaded with 

O 

a density of loading A in a chamber of capacity 6'. Therefore, 

6 '— = initial air space, 

o 


Hence equation (c) becomes 

SA 


5 - 


S{ 


b -p 8 .oli 1 _ L ) 

1 5-xa' ‘ 


Let 

Then 




= S*. 




§• 


By experiment x and y have been determined to have the value 
Hence 


b- 




( 9 ) 


91 . To obtain the value of the pressure we differentiate the 
velocity equation, which gives the acceleration of the projectile. 
This multiplied by the mass of the projectile will give the total 
pressure on the base of the projectile producing velocity * 
( f—ma ), which, divided by the cross-section area of the bore will 

* Some of the pressure of the powder gases is used in rotating the shell. 






Naval Ordnance 


76 


give the pressure per unit area on the base of the shell pro¬ 
ducing velocity. 

The process is as follows : 

Differentiating equation (7), 

dz' _ab du _ abz’ _ a 2 bu 
dt (b + u) 2 dt ( b + n ) 2 (b + u ) 3 

This is acceleration. The mass of the projectile is 1 , and A is 

«S 

the cross-section area of the bore. Hence 


D_ W Y I y, dv _ w v a 8 ^ 
g X A X dt ~gA (b + u) 3 ' 

Dividing by 2240 to get the value in tons, we have 


P- 


zva 2 bu 


2240gA (b + u) 3 


(10) 


92 . This value of P is the pressure producing velocity exerted 
on the base of the projectile at any point, u, but owing to friction 
the force necessary to drive the rotating oand through the rifling, 
heating, expanding the gun, etc., the pressure by gauge in the gun 
may be expected to be considerably higher. Such is, in fact, the 
truth, and it has been found that by multiplying the value of P 
from equation (10) by 1.12 it is brought to correspond very well 
with the values found by actual firing. That is. 


P < ma.r ) X 1.12 — P ( 


max)(gauge)* 


(u) 


Since P is a maximum when u = b/2 (see definition in para¬ 
graph 90), substituting this value for 11 in equation (10), we have 


P 


( mar) - 


_w_ a 2 b( b/2 ) _ w orb 2 

2240 g A (b + b/2) 3 2240gA 2 


8 

27b 3 ’ 


or 


P ( ma.T ) — X 


crzv 


-/ 


2240gAb ’ 


(12) 


which expression gives the value of the maximum pressure on the 
base of the shell producing velocity. 

93 . We have no means of measuring the maximum pressure on 
the base of the projectile, but can very easily measure the maxi¬ 
mum pressure in the bore of the gun by using pressure gauges. 
Consequently, equation (12) may be changed to a more con- 








Elementary Interior Ballistics 


77 


venient form for use by substituting for P (max) its equivalent 

P ( max)(gauge) 


1.12 


from equation (n), which will give 

P(max)(gauge) _ 4 .. Cl~ZV 

— X- 


1.12 27 2240 gAb 

Now clearing the expression for b, we have 


_ 4?a 


b=‘ 


X 


1.12a- 


27 22^0gAP (max) (gauge) 

which gives a means of determining b by measuring the maximum 
pressure in the bore. But the expression is in terms of a, which 
is undesirable. To eliminate this we substitute in (13) the value 
of a found from equation (8). which gives 


4 W 


1.12 


b= x , n 

27 22^0gA P ( ma .x ) ( gauge) 


Now substituting for A its value from equation ( 1 ), i. e., 


27.680 

S' 


. we have 


1.12 X 6823' x w X — 
u= ^ x w S ‘ 


2 ; 


2240gAP t 


maa ?) < ga ugr ) 


_ 4 x 1 . 1 2 x 6823 * X 27 . 68 ° X o5"_ 

27 X 2240 X 32.1 55 X A X S* X P { max)) gauge) 


(d 


For any given gun A and 5 are known, and, therefore, if we 
take 


Q 


_ 4 x 1.12 x 6823' x 27.68" 


27 X 22 40 X 32.155 xAx S« 


(14) 


eijuation (d) may be written 

g* —_ (I5) 

1 (max)(gauge) 

94 . This value, Q, is different for each gun. but is constant for 
all powders in any given gun. The values of Q for all guns in our 
service have been determined and tabulated. The values of Q 
are given below, together with the value of U, or total travel of 
projectile in the bore from origin to muzzle. 

(Note.— Q is tabulated in terms of its logarithms and U is, of course, 
in feet.) 



















78 


Naval Ordnance 


TABLE I. 


Gun. 

Mark. 

Log Q. 

U (total). 

16-inch, 45. 


9-24345 

51.821 

14-inch, 50. 

iv 

9.36818 

50.250 

14-inch, 45. 

I 

9.38686 

45-204 

13-inch, 35. 


9-45155 

31.211 

13-inch, 35. 

1 and II 

9.45226 

31.193 

12-inch, 50. 


9.52310 

42.X65 

12-inch, 45. 

V-5 and VI-3 

9-52330 

37-743 

12-inch, 40. 

111-3 

9 - 5 I 25 I 

32.751 

12-inch, 35. 

I 

9-53776 

28.907 

12-inch, 35. 

II 

9-53776 

28.851 

10-inch, 30. 

I 

9-73723 

20.954 

10-inch, 40. 


9.70761 

27.302 

8-inch, 35. 


9.98716 

20.537 

8-inch, 45. 


9.94946 

24.971 

7-inch, 45. 


0.09235 

21.651 

6-inch, 40. 

IV 

0.30014 

17.162 

6-inch, 40. 

VII 

0.30014 

17.188 

6-inch, 45. 

IX 

0.30014 

18.512 

6-inch, 50. 

Arms. V 

0.31411 

22.312 

6-inch, so. 

VIII 

0.26651 

20.732 

5-inch, 40. 

II and III 

0.50802 

13.982 

5-inch, 50. 

V 

0.46379 

17.917 

5-inch, 50. 

VI 3,000 f. s. 

0.46488 

17.917 

5-inch, 51. 

VII and VIII 

0.46530 

17.929 

4.7-inch. 


0.58832 

17-173 

4-inch, 40. 


0.75121 

11.198 

4-inch, 50. 

VII 

0.70364 

14.018 

4-inch, 50. 

VIII 

0.70364 

14.018 

4-inch, 50. 

3-inch, F. G.... 

IX 

0.70364 

1.16810 

14.018 

4-947 

3-inch, L. G... . 

IV 

1-13463 

5-233 

3-inch, 50. 


1-03594 

10.658 

6-pounder. 


1.38967 

8.452 

3-pounder. 


1-56387 

6.560 

i-pounder. 


1.89975 

4.406 


For gun-design work where A and N are variables it is con¬ 
venient to use a different constant as follows: 

n - - 186.53 

AxS *• 

95 . In equation (10) for any specific case we know a and b, 

• ci“ b • 

therefore the quantity - —-is a constant and for plotting: a 

2240 gA 1 & 

curve of pressures on the base of a projectile we substitute for 
this quantity the constant R p , which is, of course, constant for the 
whole curve. 





















































Elementary Interior Ballistics 


79 


Equation (io) may then be written 


p — RpU 

( b+uy ’ 


06 ) 


which expresses the relation between the pressure on the base of 
the projectile at any point in the bore, and the travel, u, to that 
point. 

This pressure will be a maximum when u = b/2, or 


R p b 

D _ 2 _ 4 Rp . 

JJby - 2yb 2 

From this 

r> 2jb~P(max) 


But P (max) is the maximum pressure on the base of the pro¬ 
jectile producing velocity, which we cannot measure readily. 

Therefore, substituting for P (max) its equivalent, ma *^ g “ ugp - - . 

from equation (n), which we can measure, we have 


R 


2jb~P 


(max) (gauge) 

X 1.12 


(17) 


96 . This is still the value of R for a curve of pressures on the 
base of the projectile. -But we desire to draw the curve of pres¬ 
sures acting on the gun in order to check the pressures on the 
gun against the corresponding strength of the gun that we may 
know whether or not the gun is safe, i. e., whether or not the 
“ powder fits the gun.” 

We know the pressure in the bore, i. e., on the gun, will be 1.12 
times the pressure on the projectile, or 

E(for gun) — F(for projectde) X 1.12. 

But 

F(for projectile) = • (16 bis ) 

Hence 

F(for gun) = X 1.12= ,, u V 3 xF p x 1.12. 

v (b + u) 3 (b + u) 3 









8 o 


Naval Ordnance 


Call R p x 1.12 = R g and substituting the value of R p from equa¬ 
tion (17) we obtain 



r (max)(gauge) j j2 

4X 1.12 


or 


(18) 


R g =6. 75 b 2 P 


( max) (gauge)* 


97 . The values of R found from (17) and (18) must not be 
confused. The value found from (17) substituted in (16) will 
give a curve of pressures on the base of the projectile producing 
velocity, whereas the value of R from (18) substituted in (16), 
and values of P found for successive values of u, will give a curve 
of pressures on the gun down the bore of the gun. To distinguish 
these values of R we use the subscripts p and g as shown above. 

98 . A discussion of the derivation of the Le Due formulas and 
constants is to be found in the Proceedings of the Naval Insti¬ 
tute, No. 138. They were first determined by the French, and the 
constants originally used were those for French powders. The 
formulas came to notice in a series of articles in the Revue 
d'Artillerie, 1904, being there designated as Captain Le Due’s 
semi-empirical formulas. While approximately correct for us. they 
did not give entirely consistent results, and were corrected to their 
present values by experimental work at the proving ground, 
largely by firings in cut-off guns, of which four were obtained of 
the same caliber (5-inch), so that the velocities after different 
amounts of travel of the projectile were obtained. This work was 
planned, carried out. and deductions made by G. W. Patterson, 
powder expert. They may now be considered as standard, and. 
while of course subject to revision as more exact methods of 
determination of velocities and pressures are introduced, they have 
given excellent results. A marked example of this was the case 
of the 16-inch 45-caliber gun. whose powder charge and pressure 
were determined before the gun was built. The values, on actual 
firing, were found to be very nearly exact. 

99 . Fig. 6 shows the experimental battery used, and Fig. 7 
shows longitudinal sections of the different guns in the battery. 

The standard methods of determining velocity and pressure 
now in use at the proving ground are set forth in paragraph 792 
et seq. 



Elementary Interior Ballistics 


Si 



Fig. 














82 


Naval Ordnance 


Section V.—Applications of the Formulas. 

Problems. 

100. Formulas. —For convenience the interior ballistic formulas 


most often used are grouped together. 
27.68(0 


f 


A = 


S 


8=1.672-(.0178xT.V.) (see Art. 44). 


(0 

(2) 


a • u 
b + a ’ 



P = 


R • u 


(b + u ) a * 

Rg = 6.7$b-P i 1/1(1 J)( ffUUffC)- 
P (max )( gauge ) 


P (max) — 


1.12 


( 7 ) 

( 8 ) 

( 9 ) 

(15) 

(16) 
(18) 

(n) 


P 


(max) 


4 arw 

27 x 22400 A b~ ' 


(12) 


Is the powder suitable for the gun ?—Interior ballistics finds its 
daily service use in answering this question, which, naturally, must 
be answered for each powder index manufactured. The brings 
at the proving ground give the data from which to calculate the 
powder pressure at every point along the bore. A curve of these 
bore pressures is drawn and superposed upon the strength curve 
of the gun. If the ratio f, factor of safety, everywhere along 
the bore exceeds 1.4, the powder is considered suitable for the 
gun. This work forms a large part of the daily routine at the 
Naval Proving Ground at Indian Head, Md. 

101. For every lot of powder two pressure and two velocity 
curves must be drawn. To plot the brst pressure curve a suc¬ 
cession of charges of increasing weights are bred, and the bore 
pressures measured with pressure gauges. Points are plotted 
using the weights of charge as abscissse, and the corresponding 
bore pressures as ordinates. Such a curve is shown in the lower 
right corner of the facsimile “ Powder Test Sheet,” Plate I. 







Fiom: Inspector of Ordnance in Charge. 
To: Bureau of Ordnance. 


Date. 

Time. 

Projectile. 

Powder. 

Make. 

Year. 

Lot. 

Band. 

Heated. 

Charge. 

To base. 

Width. 

Diam. 

d 

3 

Weight. 

Shape. 

Br' 

9 

Flours. 

Oct. 19 . 

Tf 

00 

N. G. F. 

. .. . 

. .. . 

ii 

4 

12,174 

12.470 

868 

Slug 

65 

66 

230 

Do.... 

8.54 

..do.. 

. .. . 


ii 

4 

12.173 

12.478 

870 

do 

65 

66 

330 

Do... 

9-05 

..do... 



Ii 

4 

12.173 

12.484 

871-5 

do. 

65 

66 

344 

Do. ... 

9 -i 6 

•.do... 

1 


Ii 

4 

TT 

IN. 

12.485 

867.5 

do. 

65 

66 

322 


NAVAL PROVING GROUNDS, 

• Indian Head, Md., 

October 25, 1915. 


POWDER TEST SHEET. 


CHAPTER III, PLATE I. 

Powder Test No. 2997. 

Powder: {Designation 1 . H. F. D p. 

\Index No. S. P. D. 1365. 




Chamber pre 

ssure. 



Muzzle 

veloci 

ty- 

Gun 12 in. 50 caliber. 














gauges. 




Chronographs. 


Mark VII Mod. 1 No. 180—L. 












I 

2 

3 

4 

5 

6 

C 

CJ 

<D 

A 

B 

C 

03 

Chamber 14611 cubic inches. 







S 





Rifling: Depth of grooves .075. 












7 94 

7-86 

7 19 




7. 66 

2130 

2130 

2130 

2130 

number of grooves 72. 





16.20 

16.84 

16.84 

16.44 

16 68 

16.76 

16.63 

2872 

2872 

2872 

2872 

pitch 1/50 to 1/32 

18.89 

19.08 

18 71 

18.08 

18.71 

17.99 

18.58 

2967 

2967 

2967 

2967 

Number of sections 4. 

15-30 

15-59 

15 73 

15.14 

15-66 

15-66 

I5-5I 

2824 

2824 

2824 

2824 

Ignition per section 300 grams C. P. 












Previous rounds : / actl ?al 52. 

Lequivalent service 53.2. 












Erosion loss : -f^ S- 
[2.0 tons. 


Weather: Fair. Temperature, F.: dry bulb 60.5; wet bulb 59.5. Time in dry-house: 116 days at 39 4 C 

kor/n-vml-n* r r „ a zfAO T? Ill' 1 1 ... * Ozf • H 


Barometer 30.11 at 66° F. 

Cotton: Tennessee fiber. 

Die: diameter.985 

number of pins 7 
pin diameter.. .072 

Length of cut. 1.75 

Nitration.12.64% 

Diphenylamine.45% 


Wind 0 knots at o’clock 

(XII o’clock head wind.) 

Dry grain: length. 1.61 

diameter.697 

Diam. perforation.057 

Average web.132 

Outer web.128 

No. grains per lb.30.6 


German test, 135' C.< 



66 days without heat. 

/Violet 95' 

[Explosion 5 hrs. + 
Surveillance test 65 .5 C. days. 

Heat test of pyro 65°. 5 C. 35 + minutes. 

Total volatiles,/ - dry-house condition 6.73% 

W. P. method,[as received 7.00% 

Original firing test, j° ate ,, AT This date ‘ 

LPecord No: 

Lot contains 100,123 pounds. 

Disposition: 100,123 pounds to Naval Mag., Lake w 
Denmark, N. J. 

H 
O 
O 

EH 


3000 


VELOCITY AND PRESSURE CURVES. 


Bureau Assignment. 
12"—50 
Mk. VII. 
2,900 f. s. 
1,200 gms. 
(even lbs.) 323 lbs. 

17.5 tons. 


P. G. ASSIGNMENT. 
Gun : 12"—50 cal. 


Muzzle velocity : 2,900 f. s. ^ 
Ignition: 1,200 gms C. P. O 
Charge: 322.5 lbs. 


Pressure: 17.55 tons. 


> 

W 

k) 

KJ 

N 

£5 

s 


Curve of bore pressures. 



H 3 

W 

K) 

01 

co 

CJ 

fa 

M 

H 

O 

03 

H 3 

H 

& 

CO 

£> 

Cl 

> 

ta 

w 

>—1 

a 

W 

































































































































































































































Elementary Interior Ballistics 


83 


* 

Os 

it 

ft 

S 3 

* 

K* 
y> K 

^ <0 

S'! 


k 

* 1 


<0 


L 


<0 

$ 

<0 

11 

• ct> 

jj" 

VJ 

„ I 

V 


if 


w 

00 

* 

§ 

•1 

>1 

£>• 


od eo 

**K. 

0 n 

k<* 

<J 

% 1 
*Q 


s 

u 


$ 

5 * 

It 
>J 
8 
£ 

3 * 

« 

K * K 
r- «o 

* v> 

k » 

*« 

k 

3 

* 1 


fT 


£ 


cj 

r-r 


Ay\oo -68 ‘iS3 -S' 

28 & "£/ =/) 'A/no 7 7nj '7&^> Otr 







































8 4 


Naval Ordnance 


102. To plot the first velocity curve, for each successive charge 
fired the resulting muzzle velocity (as well as bore pressure) is 
measured. Using the weights of charge as abscissse and the 
corresponding velocities as ordinates, points are plotted and the 
curve is drawn through the points. An example of such a curve 
is shown on the “ Powder Test Sheet,” Plate I. 

103 . The firing of successive increasing weights of charges 
thus gives simultaneously the data to plot the first pressure and 
first velocity curves, and they are plotted together on the same 
cross-section sheet, the “ weight of charge ” scale being common 
to both curves. 

104 . After drawing these first pressure and velocity curves, 
and before assigning the service charge for any gun, the fact 
must be taken into consideration that the power is generally of 
necessity proved in guns that have been fired before and usually 
many times, while the charge to be assigned is one that in a new 
gun will give the desired muzzle velocity. Therefore the wear of 
the gun must be allowed for. The exact loss due to this wear has 
been determined from many actual firings, and has been tabulated. 

In the case illustrated the tables showed that the loss due to 
erosion in the gun used was 83 foot-seconds velocity, and 2 tons 
in pressure. Therefore to get the curves as they would have been 
in a new gun the actual curves are raised by the necessary amount, 
and the dotted lines parallel to and above the actual curves ob¬ 
tained show the curves for a new gun. It is important to note 
that this decrease of pressure due to erosion is proportionally 
greater than the decrease in velocity, i. e., erosion decreases 
pressures more, proportionally, than it does velocities. The bear¬ 
ing of this fact upon all powder tests can readily be appreciated. 

105 . In the example illustrated, for this particular gun the 
bureau has assigned a muzzle velocity of 2900 foot-seconds. 
(See “ Powder Test Sheet.” Plate I.) Therefore from the point 
where the 2900 foot-seconds line cuts the corrected velocity curve 
(?. e., the curve for a new gun) we run down to the scale of 
charges, and find 322.5 pounds for the charge necessary for a new 
gun. (In this instance this weight checks very closely with the 
bureau’s theoretical assignment of 323 pounds as given on the 
“ Powder Test Sheet.”) 

Having picked, tentatively, this weight of charge, we now run 
up to the corrected pressure curve, and find that this weight of 


Elementary Interior Ballistics 


85 


charge should give a maximum bore pressure of 17.55 t( )us. This 
being within .05 tons of the bureau’s assignment, it is safe to 
assume this charge will be satisfactory, and to proceed with the 
plotting of the second pressure and velocity curves. 

106 . The plotting of the second set ot curves is done mathe¬ 
matically, and the work of the solution is as follows: 

From equation (15) obtain b, taking log Q from Table 1. 


“ = 3 22 -5 . log 2.50853 

£ log 0.41809 

P(max)(gauge )— 17-55 . Colog 8-755 7 2—10 

Q (Table i). log 9.52310—10 

b= 16.049 . log 21.20544 — 20 

From equation (18) we obtain R g . 

6-75 . log 0.82930 

b .log 1.20544.2 log 2.41088 

17-55 . log 1-24428 

Rg . log 448446 


107 . In actual practice the omnimeter can be advantageously 
used in the solution of the remainder of the work, and at the 
proving ground it is generally used. In order to explain the solu¬ 
tion more fully, and as an example of the method required in the 
Department of Ordnance and Gunnery, the solution by logarithms 
follows. 

108 . Take various points ir. the travel of the projectile and 
calculate the bore pressures at each of these points, computing also 
the factor of safety at each of the points as the work progresses. 
The strength of the gun at the points used is taken from the 
strength curve of the gun. 

Note that the chamber must withstand the maximum bore pres¬ 
sure, no matter how far the projectile may have moved. In other 
words, so far as the chamber itself is concerned we need only 
know the gauge pressure. Also note that the maximum pressure 
does not occur when u is zero, for we use progressive powder. 
The maximum pressure is reached when the projectile has traveled 

to the point where u = ~ ■ 

We see from the curve of gun strength on the “ Powder Test 
Sheet ” that the strength of the gun at the chamber is 30.16 tons, 













86 


Naval Ordnance 


and the maximum pressure in the gun ( i . e., the gauge pressure) 

is 17.55 tons, hence /,= ^^-=1.72. This is greater than 1.4. 
/ oo 17.55 

therefore strong enough. 

Having found b above, we know the maximum pressure will 
occur when u= — or at a point 8.02 feet from the start of the 
travel. 

R g • it 


From equation (16) we have P = 


For our illustra- 


( b+.u ) 3 ‘ 

tion we will take only three points, i. e., three values of u. 


*9 — 8.1 . log 0.90849 

£> + *9 = 24.149 . log 1.38290 

3 log 4.14870-colog 5.85130-10 

Rg . lOg 448 446 _ 

^1=17-549 . log 11.24425-10 

f.,= 3 Q -46 =I .y 2 >r.4 which is satisfactory. 

1 7-55 

*9 = 20.811 . log 1.31829 

b + 19 = 36.860 . log 1.56656 

3 log 4.69968-colog 5.30032-10 

Rg . lOg 4-48 446 

P 2 = 12.68 . log 10.10307-10 


/ 3 = — t - 58>I4 which is satisfactory. 


*9 = 40.644 .. log 1.60917 

b + u 3 = 56.693 . log 1.75353 

3 log 5.26059... .colog 4-73941 - 10 
Rg . log 4-48446 


P 8 = 6.808 

/ 4 — 


I I.84 

~6W 


. log 10.83304—10 

= i.74>i.4 which is satisfactory. 


Now draw the curve of pressures and superpose it upon the 
curve of gun strength. A graphic representation of the relations 
between gun strength and bore pressures is thus obtained. (See 
lower left-hand corner of “ Powder Test .Sheet,” Plate I.) 

This is seen to be a very strong gun, and as the strength curve 
is regular it is only necessary to work out the few points as above 






















Elementary Interior Ballistics 


87 


The pressure curve is now one that agrees with the gauges. Plot 
it upon the ‘‘ Powder Test Sheet,” and lay down the strength curve 
of the gun to the same scale. The factors of safety, /, are worked 
out at the various corners of the strength curve where the value 
changes. The test sheet therefore indicates at a glance the suit¬ 
ability of the powder. If the gun is unduly stressed at any point, 
the powder must be rejected for that gun. 

Maximum pressure is thus seen to be not the whole considera¬ 
tion. It is possible for powders in some guns to be so “ slow ” 
that, while only a low pressure is obtained at the breech, the muzzle 
pressure would be sufficient to burst that part of the gun. This 
is readily appreciated if pressure curves for powders of various 
“quicknesses.” are plotted. The muzzle velocity being fixed, the 
curve areas must all be the same, and decreasing the curve ordi¬ 
nate at one end of the gun can only result in raising the pressure 
at the other end. 

Problem .—The proof of a 5-inch 50 Mk. V. gun at Indian Head 
gave as results : Velocity of 2700 foot-seconds, gauge pressure of 
15 tons, charge of 19.2 pounds of powder, shell weighing 50 
pounds. Determine the bore pressures at travels of 8, 22, and 
40 calibers. 

Ans. 14.96 tons ; 9.7 tons ; and 5.3 tons. 

The strength curve shows at these points strengths of 20.8, 14.6, 
and 6.5 tons. What is the factor of safety at these points and is 
the powder suitable for the gun? 

Ans. 1.39; 1.5 ; 1.2. The gun is too weak for this powder. 

109. To calculate reduced velocities .—Due to certain circum¬ 
stances it is often necessary to use only a part of the service 
charge. Thus it was, at the Dardanelles in 1915, necessary for 
the battleship Queen Elizabeth to use but three of the four sec¬ 
tions of the charges for her 15-inch 45 guns in order to produce 
a good (large) angle of fall on shore, while at the same time 
reducing the wear on her guns. In order that she might fire 
accurately it became necessary for her officers to calculate the 
reduced velocity and then by exterior ballistics the proper sight- 
bar settings were obtained. 

The method of procedure is as follows: 

If the density of loading for the full charge is not known this 
must be found from equation (1). Call this A^. 


88 


Naval Ordnance 


This A used in equation (8) will give the value Of for the full 
charge. 

In equation (7) we know the muzzle velocity for the full 
charge, and from Table 1 we obtain the value of u corresponding 
to the muzzle velocity (i. c., the total u). These two values, 
together with the value of a found from (8), will give in equation 
(7) the value of b for the full charge (*. c., bf ). 

The values bf and A/, substituted in equation (9), in which we 
know all the other quantities but ft, will give us the value of ft. 

ft is constant for any given powder, being dependent on the 
form and dimensions of the grain, and does not vary, as do a and 
b, with the amount of the charge (i. c., ft is independent of the 
weight of charge, and consequent density of loading). 

It must be noted that a change in the weight of charge produces 
a change in the density of loading. Therefore we must determine 
the density of loading for the reduced charge, A r . 

We now have a new value of A to use in equation (9), the other 
quantities in the right-hand member being the same as for the 
full charge, (ft constant; same powder, only reduced in quantity, 
hence same 8; N and w being of course the same since the gun is 
not changed.) Therefore, using the reduced charge A (f. e., A,-), 
we obtain a value of b for the reduced charge, b r . 

Also, using the reduced charge A in equation (8), we obtain a 
value of a for the reduced charge, a r . 

Using, now, the values of a r and b r (1. e., reduced charge 
values), u being the same as for the full charge (i. e., U for the 
same gun), we obtain a value of v for the reduced charge. As the 
value of u we should use should be the total travel, or U, the value 
of v resulting will be the muzzle velocity, or V. 

As an example of the work the following problem is worked 
out in full. 

Problem. —The firing of 38 pounds of a powder whose specific 
gravity is 1.58 in a 6-inch 50-caliber Mark 8 gun gives to a shell 
weighing 105 pounds a muzzle velocity of 2800 foot-seconds. The 
chamber capacity of the gun is 2050 cubic inches. Calculate the 
velocity that will be obtained when a charge of 30 pounds is used. 

Solve equation (1) to obtain A (full). 


^ = 38 . log 1.57978 

27.68 . log 1.44217 

^=2050 .log 3.31175... .colog 6.68825 — 10 

A/ = o.5i3i . log 19.71020—10 







Elementary Interior Ballistics 


89 


With this value of A solve equation (8) for (if. 

6823 . log 3.83398 

± f = .log 9.71020-10.Yj log 9-97585 ~ 10 

5 .....log- 1.57977 

105 .log 2.021 19 

«/w .log 19.55859-10. .4 log 9.77929-10 

af = 3882.5 . log 23.58912-20 

From (7) v — 


,-, or b + u= tLLJL whence b= 'LUL —u, 

0 + u v v 

U—U — 20.732 (Table 1). log 1.31664 

a f . log 3.58912 

V= 2 Soo .log 344716.colog 6.55284—10 


—=28.747 

v 

u — 20.732 
b f = 8.015 


log I 1.45860 — 10 


From equation (9) to find /?. 


b f = 8 .015 . log 0.90391 

(1 - = 1 - = I - -3 2 = 0.68 .... colog o. 16749 

5 = 2050 . log 3.3H75 

w=io5 . log 2.02119 

S/w . log 1.29056 

§ log 0.86037. .. .colog 9.13963 — 10 

/? . log 10.21 103—10 


From (1) we now find A for the reduced charge. 


<5 = 3° . log I-477 12 

27.68 . log 1.44217 

5 = 2050 .colog 6.68825—10 

A r = 0.405 . log 19.60754-10 

With new values of A and 6 find a,- from (8). 

6823 . log 3-83398 

A r = o.405 .log 9.60754-10. T V log 9 - 967295 -ic 

w = 3Q . log 1477 12 

W — 105 .colog 7.97881 — 1 o 

H/w . log 19-45593- 10 • -i log 9-727965-10 

Or . log 23.52924-20 










































Naval Ordnance 


9° 


With ft constant and new value of A find new value of b from 
( 9 ). 

. log 0.21103 

1 - \ = 1 - °- 4 ° 8 5 - =0.744 . log 9.87157- 10 

S/w (from above). 5 log 0.86037 


£>,. = 8.7693 . log 10.94297—10 

With values of a and b for the reduced charge find V from (7). 
. log 3-52924 


Or 


u=U = 20.732 . log 1.31664 

N+it = 29.501 . 


log 1.46982-colog 8.53018—10 


F = 2377.2 . log 13.37606-10 

The muzzle velocity for the reduced charge will be 2377.2 f. s. 

Having thus determined the velocity that will be obtained, it 
becomes necessary for the gunnery officer to determine what sight- 
bar range to use for the actual range at which the firing with the 
low charge is to be done. This is a problem in exterior ballistics, 
the solution of which will be found in “ The Groundwork of 
Practical Naval Gunnery, or Exterior Ballistics.” 

110 . To determine the charge for one gun, using powder 
designed for another, we firs: assume a density of loading, rather 
than a weight of charge. This is because the Department has set 
limits for the density of loading for each gun, and also because, 
by comparing the two calibers under consideration, we can arrive 
more quickly at an assumption, remembering that the powder of 
one caliber will always be relatively quicker in a gun of larger 
caliber, and vice versa. 

After the weight of charge has been determined a number of 
pressures down the bore must be determined, and compared with 
the strength of the gun at the points, in order to know the factor 
of safety, and to be sure the powder fits the gun as well as possible. 

Let the subscript 1 designate the values determined for the gun 
for which the powder was made, and the subscript 2 designate 
similar values determined for the gun in which we desire to use 
the powder. 

If not already known, the value of A x is first found from 
equation (1), using 












Elementary Interior Ballistics 


9i 


The value of a, is then found from (8). using w,, w,, and A,. 

Knowing V 1 and U lt and using a lf the value of b x is found front 
(/)• 

With by. A,, S lt w lt and 8 the value of (3 is found from (9). 

A value of A., is now assumed, and with this the value of b., is 
found from (9), and w 2 from (1). (/3 and 8 being the same as for 
the original gun, .S 2 and w., being for the new gun.) 

With A.^ and w 2 the value of a., is found from (8), and with a., 
and b. 2 the value of P ima x) 2 is found from (12). This value 
in (11) gives the maximum working pressure in the gun, 
P imax)(gavgc)o- 

Rg 2 is then found from (18), which with successive values of u 
in (16) gives a series of pressures down the bore. These pres¬ 
sures are compared with the strength of the gun (in which the 
powder is to be used) at the same points to be sure the charge is 
of the proper size. 

If the assumed density of loading is not correct (?. c., if the 
'comparison of pressure and strength at the various points does 
not show the required factor of safety) a new value of A 2 must 
be assumed and the solution he repeated until a weight of charge 
is found that will fit the gun as well as possible. 

To illustrate the procedure the following problem is solved: 

Problem. —A charge of 90 pounds of a certain powder whose 
specific gravity is 1.56, fired in a 10-inch 30-caliber gun, having a 
chamber capacity of 6700 cubic inches, gives a projectile weighing 
510 pounds an initial velocity of 2000 foot-seconds. What weight 
of this powder can be used in a 12-inch 50-caliber gun whose 
chamber capacity is 14,611 cubic inches, and whose shell weighs 
870 pounds; the maximum allowable density of loading for this 
gun being 0.669, and the maximum allowable working pressure 
being 17.5 tons? 

From equation (1). 


27.68 . log 1.44217 

^ = 90 . lo § 1 -954^4 

6^ = 6700 .log 3.82607-colog 6.17393-10 

A 1 = o.37i8 . log 9.57034-10 








92 


Naval Ordnance 


From equation (8). 

6823 . log 3 - 8339 8 

<i, =90 .log 1.95424 

Wj = 5io .log 2.70757 

fij/wj .log 9.24667-10.. 4 log 962333-10 

A, .log 9.57034-IO. . tV log 906420-10 

a t . log 23.42151-20 

From equation (7). 

a, . log 3421 5 1 

19 = 20.954 (Table 1). log 1.32126 

V 1 = 2000 .log 3.30103-colog 6.69897-^10 

antilog 27.652 . log 11.44174—10 

( ) u 1 —20.954 

£q = 6.698 
From equation (9). 

fq = 6.698 . log 0.82595 

A t = 0.3718 .log 9.57034-10 

8=1.56 .log 0.19312 

a 1 /8 = o. 23835 .log 9.37722-10 

1 —A x /S = o.76165 . .log 9.88176—10... .colog 0.11824 

59 = 6700 . log 3.82607 

«q = 5io .log 2.70757 

S 1 / zv 1 .log 1.11850 

I log 0.74567.colog 9.25433-10 

/?= 1-579 . log 10.19852-10 

A powder designed for a 10-inch gun will be relatively fast in a 
gun of larger caliber, such as a 12-inch, which is given in the 
problem. The maximum density of loading allowed by the 
Department is 0.669. If this density of loading is used the result¬ 
ant pressure (max) is bound to be too great due to the quickness 
of the powder. As a first assumption, then, let us try a density 
of about half of the allowable, say 0.34. 




























Elementary Interior Ballistics 


93 


From equation (9). 


P =l -579 . log 0.19852 

A 2 = 0-34 .1059.53148—10 

3 = 1-56 .log 0.19312 

A 2 /8 = 0.21795 .log 9.33836-10 

1 —A 2 /S = 0.78205 . log 9.89324—10 

6\,= i46n .1054.16468 

Zl '., = 870 .log 2.93952 

S 2 / w 2 .log 1.22516.§ log 0.81677 

b 2 = 8.ioi . log 10.90853—10 


From equation (1). 

—14611 . log 4.16468 

A 2 = °-34 . log 9.53848—10 

2 7-68 .log 1.44217.colog 8.55783-10 


179.47 . log 22.25399—20 

From equation (8). 

682 3 . log 3.83398 

"2=17947 .log 2.25399 

w 2 = 870 .log 2.93952 

"2M .log 9.31447-10. . 4 log 9.65723-10 

^2 = 0.34 .log 9.53148-10. . T V log 9.96096-10 

«2 . log 23.45217-20 


From equation (12). 


a . 

. . .log 3-45217- - • 

...2 log 6.90434 

4 . 



w„ — 870 . 


.. . log 2.93952 

27 . 

•••log 143136-.. 

.. . colog 8.56864 — 10 

2240 . 

• • - log 3-35025. • • 


^ = 32.i55 . 

. . .log 1.50725. . . 

...colog 8.49275—10 

A—ir-r 2 3.1416 . . 

• • -log 049715- • • 

...colog 9.50285—10 

r 2 = 2>6 .. 

...log 1.55630... 

. . .colog 8.44370— 10 

b . 

• • - log 0.90853. . . 

...colog 9.09147—10 

P ( max )2 . 




From equation (11). 

Pima *) 2 . log 1.19508 

1.12 . log 0.04922 

P(max)(gaugc )2 17-55 . l°g 1 - 2443 ° 



















































94 


Naval Ordnance 


This value of the maximum working pressure, 17.55. is almost 
exactly equal to the limit of pressure laid down for the gun, hence 
the assumed value of the density of loading is satisfactory. 
Therefore any charge of this powder not exceeding 179 pounds 
will not produce an excessive maximum pressure. Had the value 
of the maximum pressure been too great another assumption of 
A, would have been required, and the work repeated. Had the 
pressure been much below that allowed, and a greater pressure 
been desired, the work would have been repeated in the same 
manner as above, using a greater value of A... 

The work above has given a weight of charge that will not 
produce an excessive maximum pressure. It now remains to 
check up the pressures along the bore. (In this particular case it 
is evident that as the maximum pressure is safe all the others will 
be also, and no further work is necessary. This is not always the 
way of the matter.) 

The further work, then, is to calculate a series of pressures, 
compare these pressures with the corresponding strengths of the 
gun, and obtain the values of the “ factors of safety.” The 
procedure is exactly like that shown above in Art. 108. 

111 . Velocity given by same powder in guns of different 
caliber. 

Once the limiting density of loading, and consequent maximum 
weight of powder charge, has been determined for a gun other 
than that for which it was designed, the problem is to find the 
velocity any charge of this powder (equal to or less than the 
maximum allowable) will give in the gun in which it is desired 
to be used. 

The first part of this solution is exactly like the first part of the 
solution for the maximum weight of charge allowable to use. To 
show clearly the whole procedure that solution will not be con¬ 
sidered here, but the whole problem will be solved. 

As before, let the subscript 1 denote values for the gun for 
which the powder was designed, and the subscript 2 the values 
for the gun in which the powder is to be used. 

from equation (1) the value of A, is found. Using this value 
with w,, and it', in (8) gives a,, which used with the values for 
gun 1 in (7) will give b x . This b x , with the other values necessary 
for gun 1 in (9), will give 

/? is, of course, the same for both guns. 





Elementary Interior Ballistics 


95 


With the charge of powder decided upon (not greater than the 
maximum allowable), and using S 2 , the value of A 2 is found from 
(i). With A 2 , and the other necessary values for gun 2, the 
values of a 2 and b., are determined from (8) and (9), respectively. 

With a.,, b 2 , and U 2 the value of F, is found from (7), which 
is the quantity whose value is desired. 

As an example of the work the following problem is solved : 

Problem .—A charge of 90 pounds of a certain powder whose 
specific gravity is 1.56, fired in a 10-inch 30-caliber gun, whose 
chamber capacity is 6700 cubic inches, gives an initial velocity of 
2000 foot-seconds to a shell weighing 510 pounds. If 175 pounds 
of this powder is fired in a 12-inch 50-caliber gun whose chamber 
capacity is 14,600 cubic inches, what velocity will be given a shell 
weighing 870 pounds? 

From equation ( 1). 

27.68 . log 1.44217 

<^ = 90 . log 1.95424 


S x — 6700. 

. . .log 3.82607- 

. .colog 

6.17393-10 

^ = 0.3718 . 


• • log 

9.57034-10 

From equation (8). 

6823 .*. 

Wj = 9®. 

w i = 5 io . 

..log 1.95424 
. .log 2.70757 

• • log 

3.83398 

«>i/Wi . 

. . log 9.24667— 10. 

• • 1 log 

9-62333-10 

. 

• log 9.57034-10. 

•tV log 

9.96419—10 

a x = 2639.4 . 

From equation (7). 

b = ^--U. 

•. log 

2342150-20 

. 



342150 

U x — 20.954 (Table 

1). 

log 

1.32126 

F, — 2000 . 

• • • .log 3-30103. • . . 

. .colog 

6.69897— 10 


antilog = 27.652 . log 11.44173—10 

( 7 -)E/i = 20-954 





















Naval Ordnance 


96 


From equation (9). 

^ = 6.698 . log 0.82595 

A i = o- 37 l8 .log 9 - 5703 I-!<> 

8=1.56 .log 0.19312 

A 1 /8 = o. 23834 .log 9.37719-10 

1 — A 1 /8 = o. 76 i 66 ... .log 9.88176—10. .colog 0.11824 

^ = 6700 .log 3.82607 

^ = 510 .log 2.70757 

S 1 /w l .log 1.11850 

f log 0.74567.colog 9.25433-10 

P= 1-579 . log 10.19852-10 

From equation (1). 

27.68 . log 1.44217 

w 2 = 175 . log 2 - 2 43°4 

So = 14600 .log 4-16435.colog 5.83565-10 

A 2 = o.33i 8 . log 9.52086—10 

From equation (8). 

6823 . log 3.83398 

^=175 .log 2.24304 

«l = 8 70 .log 2.93952 

< 5 2 M .log 9.30352-10.. .| log 9.65176-10 

Ao = o. 33 i 8 .log 9.52086—10. . T V log 9.96007—10 

02 = 2791.3 . log 23.44581-20 

From equation (9). 

/^ — 1 -579 . l°g' 0.19852 

a 2 = c. 33 i 8 .log 9.52086—10 

8=1.56 .log 0 .19312 _ 

40/8 = 0.21268 .log 9.32774—10 

1 — 43/8 = 0.78732 . log 9.89615—10 

So =14600 .log 4-16435 

IV 0 = 870 .log 2.93952 

S,/w 2 .log 1.22483.| log 0.81655 

60 = 8.1511 . log 10.91122—10 








































Elementary Interior Ballistics 


97 


From equation (7). 

00 = 2791.3 . 

U 2 = 42.165 (Table 1). 

b 2 — 8.151 

b+ [7 = 50.316 .log' 1.70170 

V 2 = 2339.2 . 


log 3445 s 1 
log 1.62495 

colog 8.29830—10 
log 13.36906— IO 


The value V 2 is, then, the velocity that will be given by the 
powder from gun 1 when used in gun 2. The sight-bar setting 
to use to hit at any desired range is a problem whose solution 
lies in the field of exterior ballistics. 

112 . Problem on gun design. —Certain requirements that a 
new gun must fulfil are laid down before any work on the design 
is commenced, these requirements being taken from a considera¬ 
tion of the dimensions of guns already built. 

Suppose a new 12-inch 50 gun is to be designed. The following 
approximate requirements will be laid down: 

Shell = 870 lbs. Max. working pressure =17 tons. 

I. V. = 2900 f. s. A to be not greater than .65. 8 = about 1.55. 

Chambrage= 1.25. Length of chamber to be from 6 to 7 times 
its diameter. 

Then the problem that must be solved before the design can be 
even roughly sketched is to determine— 

a. The weight of charge, w. 

b. The capacity of the powder chamber, S'. 

c. Approximate dimensions of the powder chamber. 

d. The characteristic of the powder, /?. 

e. At least five points of pressure and velocity curve, and con¬ 
struct the approximate curves. 

(a) Before the logarithmic and arithmetical work can be 
started certain new equations must be derived from those already 
deduced. This,work is as follows: 

Dividing both numerator and denominator of the right-hand 
side of equation (7) by b there results 

a. u 


8 










98 


Naval Ordnance 


A new symbol is here introduced, i. c., M — hence 

a ■ M 


V = 


i +M* 


or 


(i +M)-V 
M 


(A) 


(b) From the assumption of the value of M it follows that 
b= ^, and substituting this value of b in equation (12) it follows 
that 


P 


4 x a 2 x zv x M 


i max ) — ~~ 


whence 


27 x 2240 xgxAxU’ 


_ | 27 x 2240 xgxAxU xP ( max) 

" \ 4 xzvxM 


Equation (B ) may be written 


\ M 


(B) 


(C) 


where K is taken equal to all the cjuantities in efiuation (B) that 
e constai 
That is, 


are constant for any given gun. 


- _ 27 • 2240 • g • A • U • P< mat 


K = 


r) 


4 • zv 


(19) 


Equating equations (A) and (C) gives 
~K J 


\ M ' M 


or 


1 +M). 

K- M = V 2 (i+2 M + M-) ; 
M 2 + 2M+i-^ =0, 


which quadratic being solved 


1 =0, 











Elementary Interior Ballistics 


99 


(c) In solving logarithmically the two factors in the numerator/ 
of (20) are solved separately, or 



whence 


and 



M = 


— x + y 
2 


(20a) 


(d) Equation (8) gives a value of a which we may equate to 
equation (A), whence 


or 


Whence 


or 


a = 6823 • A* • 
V — 6823 • A* • 



/«\i_ V(M+l) 

V w ) 6823 • A* • M ’ 


' V( M- fi) ' 
6823 • A* • M 


(21) 


(e) The logarithmic work follows. 

Solution .—The diameter of the powder chamber may be, by the 
conditions, = 1.25 x 12, or =15 inches, and as a point to start from 
this diameter is used. It is not the final diameter. 

The-length of the powder chamber will be between 15x6, or 
90 inches, and 15x7, or 105 inches. 

Take 93 inches as a first trial length. The total length of the 
gun take as 600 inches. The total travel of the projectile, U, is 
then 600 minus 93 or 507 inches, which is 42.25 feet. 

Pdnaxm/auff,) has been given as 17 tons, hence, from equation 
(11), P(«ax) is 15.18 tons. 

From equation (19) find K. 


27 . 

2240 . 

^ = 3-- 1 55 (at proving ground) 

A= (3.1416x36) 3.1416 . 

36 sq. in... . 
[7 = 42.25 ft. 


P ( max) — 1 5 • 1 O . 

4 .1.. . log 0.60206 

IV = 870 .log 2.93952 


log 

log 

log- 

log 

log- 

log- 

log 

colog- 

colog 


143136 

3-35025 

1-50725 

0.49715 

1-55630 

1.62583 

1.18127 

9-39794-IO 
7.06048— 10 


K 


log 27.60783 — 20 
























loo 


Naval Ordnance 


From equation (20a). 

K . log 7 60783 

V (specified) =2900 f. s...log 346240 

2 log 6.92480. .colog 3.07520—10 

— =4.8198 . log 10.68303—10 

IS 

X = 2— — =—2.8198 ... .log( — )0.45022 
V 2 

( K \ 2 

2 ~v*) = 7-9513 . 2 log 0.90044 

minus 4.0000 

3 - 95 I 4 .log 0.59675 

y = 1.9878 .| log 0.29838 

y — x = 4.8076 

l(y — x ) = 2.4038 — M 

M + 1=3.4038 


From equation (21) 
V = 2900 f. s.. .. 
3.4038 .. 


M +1 

6823 .. 

A (specified) 0.65 


. .log 9.81291 — 10 
tV log 9 - 9844 I - 10. .colog 
M — 2.4038 .log 0.38089.colog 


From equation (1). 
27.68 . 


A = o. 65 .lig 9.81291 — 10. 

A = 14419 cu. in. 


log 

3.46240 

log 

0.53196 

colog 

6.16602— 10 

colog 

0.01559 

colog 

9.61911 — 10 

log 

9.79508-10 

2 log 

19.59016 — 20 

log 

2 - 9395 2 

log 

22.52968 — 20 

log 

1.44217 

log 

2.52968 

colog 

0.18709 

log 

4.15894 


The assumed diameter was taken as 15 inches, and from this 
a length of 93 inches was found for the length of the powder 
chamber. Keeping this length of chamber fixed, the true diameter 
of the chamber is found. 
























Elementary Interior Ballistics 


ioi 


or 


Space = Area x Length = 


7r • I.)~ 

4 


x 93 > 


4 . 

D= IxJL. 

\ 93 ' *■ 



A—14419 . 



••• log 4-15894 

93 . 


1 .96848 . . . 

...colog 8.03152—10 

3.1416 .... 


O.49/I5. . . 

.. . colog 9.50285 — 10 

D= 14 ... 



log 22.29537-20 


That is, the proper diameter of the chamber, for a chamber 
length of 93 inches, to give a density of loading of 0.65 with a 
charge of 338.5 pounds of powder is 14 inches. Hence the 
approximate dimensions of the chamber are 93 by 14 inches. 

These dimensions may be changed as the work on the design of 
the gun progresses. Some other value of the density of powder 
or loading, or for structural reasons, the dimensions may require 
change. 

Any change will require new values of K, M, etc., to be found, 
i. e., a new solution from the beginning. 

The “ chambrage ” being the ratio of the diameter of the cham¬ 
ber to the diameter of the bore gives |4 = 1.166, which, being less 
than 1.25 as specified, is satisfactory. 

The next step is to determine ft from equation (9), having 



u = 42.25 . 


• log 

1.62583 

M — 2.4038 . 

log 0.38089. 

. colog 

9.61911 — 10 

A = 0.65 . 

.. . .log 9.81291 — 10 



8=1.55 (specified) 

.. .log 0.19033 



A/S = o.4i935 .... 

.... log 9.62258— 10 



1—A/8 = 0.58065 . 

log 9.76392-10. 

.colog 

0.23608 

S— 14419 . 

• • • - log 4-15899 



w — 870 . 

.... log 2.93952 



S/w . 

.. . .log 1.21942 
§ log 0.81295. 

.colog 

9.18705-10 

0 = 4.6566 . 


. log 20.66807 — 20 






















102 


Naval Ordnance 


(f) Having secured the foregoing results and seeing that they 
are within reason, the gun can be laid out along these lines. Then 
the gun may he altered in various dimensions for various reasons. 
If this is done, new calculations must be made. 

To construct the pressure and velocity curves, U as determined 
was 42.25 feet. Select five points to use. Take, 3, 8, 15, 24.. and 

36 feet. Since M — 2.4038= b— 17.6, 

o 

(A bis) 


“5=36 

b + n= s S3.6 
log= 1.72916 
8.27084 
3-61347 
1-55630 

3.44061 
1-5=2758 f. s. 


a=? 9 °° (M+ 0=^00x3^35 = 

M ' 2.4038 J 

the velocity curve is calculated. 


T r • an 

Using *'= b+T t 

112—8 

£> + 1(3 = 25.6 
log= 1.40824 
8.59176 
3 61347 
.90309 

3.10832 
7-0=1283 f. s 


1(3=15 

1( 4 = 24 

b+ 1(3=32.6 

fc + i( 4 =4i .6 

log= 1.51322 

log= 1.61909 

8.48678 

8.38091 

3-61347 

3-61317 

1.17609 

1.38021 

3.27634 

3-37459 

1-3 = 1889 f. s. 

1-4—2369 f. s. 


Ml =3 

b + «i=20.6 

log= 1.31387 
colog 8.68613 
a log 3.61347 
u log .47712 

2.77672 
*'1=598 f. s. 


With these points the velocity curve may be drawn. 

The next step is to determine the pressures at these points. 
From equation (18). 

6-75 . log 0.82930 

b= 17.6 .log 1.24551.2 log 2.49102 

P (.max) (gauge ) = I / . log 1-23045 

R s . log 4-55077 


From equation (16), using the same progressive values of u, 


Ml =3 

b+u=2o-6 
log 1.31387 
3 log 3-94161 
colog 6.05839 
R log 4.55077 
u log 0.47712 
log 1.08628 
^1=12.198 


m 2 =8 

&+ m =25-6 
log 1.40824 
3 log 4-22472 
colog 5-77528 
R log 4-55077 
u log 0.9 0309 

log I .22914 
p 2=16.949 


«s = i 5 
fl+!<=32 6 
log 1.51322 
3 log 4.53966 
colog 5-46034 
R log 4 55077 

u log I .17609 
log 1.18720 

•^3=15.389 


«4 = 24 
i> + »=4i .6 
log 1.61909 
3 log 4.85727 
colog 5.14273 

R log 4 55077 

u Jog 1.38021 
log I.07371 
p 4=11.85 


m 6 =36 
/’ + m=53-6 

'og 1.72719 

3 log 5.18748 
colog 4.81252 

R log 4-55079 

u log 1.55 630 
log 0.91959 
Pi~ 8.31 


(g) Multiply the pressures by 1.4 and the values of the ordi¬ 
nates for the minimum “ strength curve ” are obtained. 

Thus the three curves necessary before the finished design of 
the gun is adopted are found. 













Elementary Interior Ballistics 103 

A complete sketch, showing the gun and the curves therefor, 
is given for the 5-inch 50 gun, with muzzle velocity of 2300 foot- 
seconds, in Plate II. 

Plate III shows the curves for M. V. 2700 foot-seconds for this 
gun. It is evident that the curves of pressure lie too close to the 
curve of gun strength and the factor of safety is too low. At 
u = 7, the factor is found to be 1.12; at (( = 32, 1.23; and at */ = 41, 
1.26. The factor of safety is too small at the breech, at the chase, 
and at the muzzle; consequently the powder is not suitable to the 
gun ; or, more exactly, the gun is not suitable for such a velocity, 
because neither change in the charge nor in the characteristic of 
the powder could bring the factor of safety to the proper figure 
throughout. A smaller charge of a quicker powder would lower 
the pressure at the muzzle and increase the factor of safety at that 
point, but at the same time would raise the pressure at the breech 
and reduce there the factor, which is already too small. A large 
charge of a slower powder would reduce the pressure at the 
breech but would increase it at the muzzle ; hence the gun is really 
not suitable for such a velocity. The standard velocity for this 
gun is 2300 foot-seconds, with resulting curves as shown in 
Plate II. " 

113 . To determine the proper dimensions for a new powder. 

Considerable time, some three months, is required after the manu¬ 
facture of a powder is commenced before an index of it is com¬ 
pleted and ready for firing tests and issuance to the service. The 
powder must, therefore, be made on fairly accurate assumptions 
in order that it may suit the new type or caliber of gun in which 
it is to be used. 

For example, it was necessary to determine what web should be 
used for the 16-inch 45 and the 14-inch 45 and 14-inch 50 guns, 
guns larger than any previously manufactured. 

This work is done by powder experts, and no set rules can be 
laid down for the determination of ( 3 , and the “ web thickness.” 

In general, however, the procedure is as follows: 

By means of equations (7), (8), and (9) values of (3 are deter¬ 
mined for known and satisfactory powders actually in use in all 
different calibers of guns. 

That is, a is found from (8), then b is found from (7), and 
then (3 is found from (9). 


104 


Naval Ordnance 


The web thickness of each powder is also measured, and a curve 
is then plotted using the web thickness of the powder as abscissa, 
and the value of (3 for that powder as ordinate. In this way a 
great number of points are plotted, and through the points a fair 
curve is drawn. This is known as the “ (3 curve.” 

By extending the curve, its form having been determined from 
known powders, values of (3 and corresponding “ web thick¬ 
nesses ” for larger and unknown powders are found. 

It remains, then, to determine the proper value of /3 to use, for, 
knowing the value of ( 3 , the corresponding “ web thickness ” can 
he picked from the curve. 

From the results of previous experience, and firings in many 
types of guns, a maximum desirable density of loading is laid 
down by the Navy Department. With this value of A the maxi¬ 
mum weight of charge is determined from equation (i). 

Using a value of (3 from the “ (3 curve,” and the maximum 
density of loading, a value of b is found from (9). This b and 
the w corresponding to the maximum density of loading give a 
Value of P (max)(gaugc) in (15)- 

Values of w decreasing in increments of 5 pounds from the 
maximum are taken, and the corresponding values of A, b, and 
P (max)(gauge) deduced from equations (1), (9), and (15) ( (3 

remaining constant). 

The resultant pressures from (15) are plotted as ordinates 
against the corresponding charges as abscissae, and the curve 
resulting from the points is known as the “ Le Due pressure 
curve.” 

Powders are then plotted on this curve, and if the points fall 
below the curve, it being a maximum curve, they are good pow r - 
ders. Those plotting above the curve are rejected. 

The final determination of “ web thickness ” is reached by 
assuming values of (3 and w, and plotting points on the “ Le Due 
pressure curve.” When a value is found that is satisfactory the 
web thickness corresponding to the j 8 is picked oft'. 

This work is long and tedious, and no example is given here. 

Section VI. —Further Interior Ballistic Considerations. 

114 . Energy per pound of powder. —The “potential” of a 
powder is the total work that could be performed by the unit 
weight of the products when indefinitely expanded without loss of 
heat, all the heat being expended in the performance of work. 


n i 11111 1 1 [ i n 1111 1 11 11 11111 1 r rm- r i n 1 11 ■. , ■ 77 i 



5— 50 cal. GUN 

CAPACITY OP- POWDER CHAMBER 

1200 CU llsl 

WEIGHT OF" CHARGE 

•5 LBS 

WEIGHT OF- F»FROvJEKlT"ll E: 

60 UBS 

TRAVEL OF- PROJECTILE 

215 6 IN. 

MUZZLE VELOCITY 

2300 FV 3 


° — vclocity curve, i v. 230 o r s 

b - PRESSURE CURVE, EMCRCV OF" TME PROJECTILE 

C — CURVE OR maximum pressure, b X I 12. 

R ~ IYICA.IM EQUIVALENT PRESSURE. 
f — CURVE OP ELASTIC STRENGTH OP THE CUKl. 


VELOCITY IN irgCT P£R 9CCONQ 
































































































































































































5— 50cal. GUN 

CAPACITY or POWDER CHAMBER 

1200 CU IN. 

WEICMT OF CHARGE 

•9-2 LBS. 

WEIGHT OF PROJECTILE 

Oo LBS. 

TRAVEL OP PROJECTILE 

215.6 IN. 

MUZZLE VELOCITY 

2700 p. s. 


a — vcl °citv curve, i.v. 2700 r s. 

b - PRESSURE curve, ENERGY OP THE PROJECTILE, 
C CURVE OP MAXIMUM PRESSURE, bx LIE. 

^ _ K/ICA 'P J EQUIVALENT PRESSURE. 

^ ~ CUI ' ,N/C or elastic strength or the quN. 


VELOCITY IN FEET PER SECOND 








































































































































































































































Elementary Interior Ballistics 


105 


The potential of nitrocellulose has been found, by computation, 
to he about 560 foot-tons per pound of powder. 

It is of striking interest to note in connection with the potential 
of a powder that there is less stored up energy in it than in most 
of the common fuels and the chief characteristic of an explosive 
lies in its enormous rate of delivery of energy and not so much 
in the amount delivered. 

The useful work, neglecting recoil, etc., performed per pound 

of powder in a gun is the quotient of the energy stored in the 

projectile by the weight of the charge in pounds. 

£ = energy stored in the projectile, in foot-tons. 

e — energy utilized per pound of powder, in foot-tons. 

1 1 W o 1 

—- = h — v- X -- - • 

2240 - g 2240 

W X V 2 


E — bnv- x 
E 


2 X 2240 XgXo) 


(22) 


In naval guns the energy obtained from a pound of powder 
varies from 134 to 184 foot-tons. Consequently the efficiency of 
the powders varies from 24 per cent to 33 per cent or approxi¬ 
mately from one-fourth to one-third. For some few of the low- 
power smaller-caliber guns the powder energy is as high as 208 
foot-tons. The potential of the powder is reduced by many causes 
that may be defined as the passive resistances to be overcome in a 
gun. The most important of these resistances are: The forcing 
of the rotating band of the projectile into the grooves of the 
rifling; the energy of rotation of the projectile; the friction of 
the band and the bourrelet along the bore ; the resistance of the air 
while the projectile is in the bore ; the acceleration of the charge; 
the energy of the recoiling parts ; the heating of the guns ; and the 
work of expansion of the metal of the gun. 

No exact figure can be given for the various amounts of work 
expended to overcome the passive resistances, but most of the 
ballisticians agree that the total amount barely reaches 20 per 
cent of the energy of translation. 

Assuming that it reaches 25 per cent, then the total work per¬ 
formed by 1 pound of powder is. ex 1.25, or from 30 to 41 per 
cent. Consequently from 70 to 59 per cent of the energy of the 
powder is carried away in the atmosphere with the blast when the 
projectile leaves the muzzle of the gun. 




io6 


Naval Ordnance 


This energy of a powder is an uncertain quantity that varies 
with the different calibers, the weight of the projectile, and the 
square of the velocity, and, therefore, it can be neglected in the 
working up of a design of a gun, there being not much value in 
the endeavor to use it in such calculations. 

115 . Powder chamber.—In naval guns the charges of nitro¬ 
cellulose powder are generally large, and correspondingly the 
powder chambers must also be large. 

Smokeless powders can be fired at high densities of loading, 
which are only limited by the conditions of suitable powder, good 
ignition, and the necessity of loading the guns- quickly and easily. 
Some cartridge-case guns have been safely fired at a density of 
loading as high as 0.80. For bag guns the practical density does 
not exceed about 0.67. With stacked charges this may be in¬ 
creased to 0.75. 

The usual density of loading in naval guns is from 0.40 to 0.70. 

In large-caliber guns, to obtain good ignition, each section of 
the charge has an ignition charge of black powder; but if the 
ratio of the length of the powder chamber to its diameter is 
greater than about 7, that precaution may prove insufficient to 
prevent abnormal pressures. The chambrage, i. e., ratio of diam¬ 
eter of chamber to diameter of bore, should be as small as possible 
to keep down the weight of the guns and for gun strength ; a good 
average for the chambrage is between 1.1 to 1.25 for our powder. 
Experience in gun design has forced navy gun designers to the 
conclusion that they should keep as close to 1.2 as other limiting 
elements permit. In England, where the questions of chambrage 
and length of chamber have been very much discussed, it is stated 
that this can be as high as 1.45. The question of chamber design 
is very closely bound up with the question of erosion, which latter 
question is so intricate that it is extremely difficult to obtain a gun 
that gives a good velocity without a prohibitive pressure and 
excessive erosion. Our service practice in chamber design has 
always been conservative, and lies between the English practice of 
small length and great chambrage and the German practice of 
long chambers and no chambrage, being like the French practice 
of keeping moderate dimensions in both directions. 

116 . Wave pressures.—The hurling back and forth of the 
powder-gas mass from base of projectile to breech produces a con- 


Elementary Interior Ballistics 


107 


dition in the chamber, known as “ ivavc pressures," of abnormal 
pressures which, if complete ignition is delayed until the shell 
has accomplished a part of its travel, may act at a portion of the 
hore where the gun is not sufficiently strong to withstand them. 
This phenomenon is akin to “ water hammer ” in pipes under 
hydraulic pressure. The only way to avoid such conditions is to 
fill the chamber instantaneously with a burst of flame that is 
sufficient to ignite the whole charge. An unsymmetrical charge 
hinders proper ignition and thus may cause wave pressures. At 
Sevran-Livry some experiments were made to determine the 
effect of unsymmetrical charges. When the charge was placed 
loose in the chamber, the pressure jumped from its normal value 
of 13.9 tons to 34 tons per square inch. The same powder fired 
in a closed chamber at the same density of loading (0.335) would 
have given only 20.8 tons. 

As a rule, the space occupied by the charge may be considered 
as fairly distributed in the powder chamber; but with a small 
charge, keeping it close to the primer vent, the greater portion of 
the vacant space is between the charge and the projectile. This 
is more pronounced when the chamber is long and narrow, and in 
these conditions wave pressures may be produced. But we must 
not forget that the conditions necessary for wave pressures are 
the firing of a very quick powder at a density sufficiently high to 
produce about 14 tons maximum pressure. Cases of this kind 
have occurred with densities of loading of about 0.32, although 
slower powders with the same density- of loading gave no wave 
pressures. 

117 . Temperature of charge in gun.—Differences in tempera¬ 
ture of the charge affect the rate of combustion, varying directly 
with the temperature. Long series of tests have been conducted 
at the naval proving ground to determine the effect upon velocity, 
using powder at different temperatures. It is found that the effect 
varies somewhat with the size and grain of the powder, but in 
general it may be taken that for every increase of i° F. in tem¬ 
perature there is occasioned an increase in velocity of 2 foot- 
seconds. 

118 . Solvent and moisture.—As solvent and moisture may be 
considered chemical ingredients of powder, variations in the con¬ 
tent of each may be expected to produce changes, such as are 


io8 


Naval Ordnance 


produced by differences in nitrogen content. This is found to be 
tbe case, experimentally; within ordinary variations moisture 
causes the same effect as solvent, or, as it increases, makes the 
powder slower. 

119 . Temperature of metal in gun after repeated firing.— 

Numerous tests have been made to determine the temperature of 
the gun and mushroom head after repeated firings. The highest 
temperatures recorded after firing 29 rounds from a 5-inch 50- 
caliber gun in 3 minutes 45 seconds were mushroom face 275 0 F., 
muzzle 304° F. These temperatures did not affect a powder 
charge left in the gun in contact with the hot mushroom for 
4 minutes. Fifty rounds from a 3-inch 50-caliber gun after no 
rapid rounds showed a maximum temperature of 394 0 F. 

These temperatures are taken in guns without operation of the 
gas-ejection system. The effect of the latter is materially to cool 
the powder chamber and bore, but tbe mushroom temperature is, 
since the breech is open during the operation of the gas-ejecting 
blast, not affected thereby. 

So far as the ballistic conditions of the gun are concerned, it is 
evident that the increased heat of the bore will heat the powder 
charge and so cause increase in velocity, provided the charge is 
left for any considerable time in the bore of the gun. When fired 
shortly after loading no increase of velocity will be produced 
from this cause. 

120 . Heat cracks.—At each discharge of a gun the metal at 
the surface of the bore is heated to a temperature that would 
cause it, if free, to expand a great deal more than it can stretch 
within its elastic limit, its free expansion being prevented by the 
outer metal (which remains comparatively cool) ; it takes a perma¬ 
nent set in compression, or, in other words, is crushed; then, 
when it cools, it is held in a state of tension by the outer metal. 
Or, in the case of a built-up gun, it is less compressed than it was. 
The usual result is that the surface of the bore, more and more, 
assumes a state of circumferential tension and ends by developing 
longitudinal cracks, called heat cracks. 

These cracks appear most prominently at the bottoms of the 
grooves of the rifling, at the root of the driving edges of the land 
when the grooves are hook shaped, and at both corners of square 
sectional grooves; and they work farther and farther into the 




Elementary Interior Ballistics 109 

metal as the use of the gun continues, but do not, in the “ accuracy- 
life ” of the gun, become deep enough to reduce the strength of 
the gun. 

121 . Erosion.—Erosion is the gradual enlargement of the bore 
and smooth wearing away of its surface by the action of the 
powder gases, beginning in rear of the rifling and extending 
farther and farther down the bore as the firing is continued. This 
wear is greatest at the origin of rifling and is about twice as great 
on the lands as in the grooves, so that its effect is to make the bore 
slightly conical from the front of the powder chamber forward 
and to gradually obliterate the rifling. 

The necessary and sufficient conditions for gun erosion are the 
intense heating of a thin film of metal at the surface of the bore 
and the rush of the gases over that surface. The temperature 
must not only be high enough, but must be maintained long- 
enough to bring the surface to the friable point. The weight of 
powder charges increases practically as the cube of the caliber, 
while the surface for absorbing the heat increases only with the 
square of the caliber. Therefore it is apparent that the bores of 
large guns are hotter than are those of guns of small caliber. The 
time action of the powder is greater in the large than in the small 
gun, being approximately proportional to the caliber of the gun. 
With similar conditions it is universally found that the erosion 
is greatest in the large caliber guns. 

That the rush of the mass of gases over the heated surface is a 
requisite for erosion is shown by the fact that the rear part of the 
powder chamber is not worn by repeated firings nor is the interior 
surface of a bomb in which powder charges are burned for experi¬ 
mental purposes. 

(1) Erosion as it actually occurs in any gun thus depends upon : 

a. Temperature of combustion and the pressure. 

b. Weight of the powder charge. 

c. Time of action, i. e., duration. 

d. Velocity of the movement of gases over heated surface. 

Erosion as it washes away the rifling and enlarges the bore near 

the origin causes a reduction in pressure and velocity with the 
ultimate condition that the obliteration of the rifling will result in 
the projectiles giving inaccurate flights. 

Erosion also enlarges the heat cracks and thus actually weakens 
the gun. 


IIO 


Naval Ordnance 


On the “ Powder Test Sheet” of the 12-inch 50 gun it is seen 
that the loss given as due to erosion is 83 foot-seconds in muzzle 
velocity and 2 tons in pressure, after but 53.2 equivalent service 
rounds. Before guns are installed on shipboard they are 
“ proved ” by firing at least five rounds, one of which is at the 
proof pressure, that is, at a pressure 25 per cent above the service 
or working pressure, though much less than the elastic strength 
of the gun. When considering the erosion wear such a round is 
counted as more than one service round while rounds fired at less 
than service pressure are counted as less than a service round. 
The decrease in initial velocity of 83 foot-seconds will cause a 
decrease in the range of this gun at 15,500 yards of 643 yards. 
So long as all guns of a ship’s battery have been fired an approxi¬ 
mately equal number of times, the erosion of the entire battery is 
constant, and a correction to the sight-bar range can be applied 
to compensate for the erosion of all the guns. 

(2) Naturally great efforts have been made to discover methods 
of combating erosion. Briefly speaking, there have been tried: 

a. Different metals for the gun tubes. 

b. Plating the gun tube with various metals and alloys. 

c. Adding to the charge, for lubrication of the bore, ozokorite 
(which also had the effect of reducing the temperature of com¬ 
bustion), graphite, and vaseline. 

d. Special seats for rotating band. 

e. Variations in rifling. 

f. Variations in powder chambers. 

Nothing has been found that will reduce it. 

The following methods have been adopted and are practiced: 

a. Using reduced charges for target practice. These are charges 
approximately three-quarters of the service charges, giving much 
lower velocities. The reduced velocity of the 12-inch guns is 2100 
foot-seconds; for all 14-inch guns, 2000 foot-seconds; for 5-inch 
guns, 2300 foot-seconds; and so on. Four such rounds erode the 
gun about as much as one service round. 

b. The twist of the rifling has been made a uniformly increas¬ 
ing one of from one turn in 50 calibers to one turn in 32 calibers 
for large guns, and one turn in 25 calibers for smaller guns. 

c. In the British Navy rotating bands are augmented by a ring 
of copper fitted over the standard band, the shell thus being seated 
at its normal position in the bore despite the erosion. 


Elementary Interior Ballistics 


i 11 


d. All major guns are now built with conical liners which when 
worn are removed from the gun, new liners then being installed, 
an operation requiring from four to six weeks for a large gun. 

122 . Life of guns.—This is the number of service rounds that 
can be fired by a gun before it loses its accuracy or loses sufficient 
energy to warrant its condemnation.* Were it not for erosion the 
life of a gun would be indefinite. There is a case of a large gun 
having been relined 14 times and still being serviceable. The 
limit of accuracy-life of the gun is set at the first “ tumble,” or 
failure, due to insufficient rotation, caused by lack of rifling, to 
fly true. 

123 . Droop.—This is caused by the lack of longitudinal rigidity 
in the gun itself or by the heat strains of unequal cooling during 
manufacture. In both cases perceptible modifications of the droop 
are brought about by firing or by the heating effect of mere 
sunshine. 

The droop of guns must be minimized as far as is practicable 
and the stiffest possible gun be constructed in order that similar 
guns may shoot alike and that the vibrations produced upon firing 
may be minimized. Hoops as long as possible are used, being 
locked together in order to reduce play at parts as far as possible. 

124 . Gun design.—To sum up how the powder affects the 
design of the gun: The quantities, caliber, weight of projectile, 
and muzzle velocity are decided upon. Particular attention has 
to be given to the powder in order that the dimensions of the 
powder chamber, length of gun, and the necessary thickness of 
tubes and hoops may be calculated. The foregoing elements con¬ 
stitute what is called the “ gun project.” A larger charge of a 
powder that is slow for a gun is manifestly required, as compared 
to the weight of charge of a quicker powder. The larger charge 
requires a larger chamber space, thus increasing the diameter of 
the chamber over that of the gun. The maximum pressure being 
less, the gun may be less strong and therefore lighter at its breech 
but stronger and heavier along its chase. If the diameter of the 
chamber is already too great, the gun must be lengthened to obtain 
the desired velocity. 

Quicker powders give very high and dangerous pressures in 
the powder chamber requiring excessive thickness of walls over 

* A 14-inch 45-caliber navy gun has fired 209 rounds with no “ tumble.” 


112 


Naval Ordnance 


the powder chamber, the gun being shorter and weaker along its 
chase, and serious erosion accompanies high pressures. The prob¬ 
able erosion, varying as it does with the pressure, figures largely 
in fixing the pressure to be allowed. 

The limiting pressure being decided upon, by methods of suc¬ 
cessive approximations the design and dimensions of the powder 
chamber are calculated from the ballistic formulas, the pressures 
at the various points of the bore and the expected muzzle velocity 
are then determined, and a conference is then usually held in 
which various conflicting elements are considered and the dimen¬ 
sions finally decided upon. 

Thus the interior ballistic formulas play the all important part 
in the design of modern ordnance. 

Next the formulas of elastic strength are used and the design 
is made. These formulas compute the points that compose the 
strength curve of the gun. 

125 . The instruments used, and method of use, to find the actual 
pressures and velocities for comparison with the pressures and 
velocities found from the foregoing formulas of Interior Bal¬ 
listics, are described in paragraph 792 et seq. 


CHAPTER IV. 

RECOIL AND RECOIL BRAKES. 

126 . All modern guns, including those of the U. S. Navy, are 
mounted so as to permit recoil when fired. 

The recoil movement is introduced to reduce the forces other¬ 
wise acting on the mount and ship's structure, and, by the reduc¬ 
tion of these forces, to produce the lightest weight of mount 
practicable for use aboard ship. 

In the case of a gun having no recoil, the force acting on the 
mount, due to the firing of the gun, is the product of the area of 
the bore and the effective powder chamber pressure. This force 
amounts to several million pounds in the case of major caliber 
guns and is of considerable magnitude for all calibers of modern 
naval guns. From this, it is obvious that, for a gun having no 
recoil, the proportions of the mount would be unreasonably large, 
making it cumbersome to handle and, on account of weight, 
unsuitable for use aboard ship. 

By permitting the gun to recoil a limited distance the forces 
which would otherwise act on the mount are greatly reduced and 
can be regulated to suit the character of the vessel for which the 
mount is designed, and thus make possible the use of larger caliber 
guns aboard ship than would otherwise be practicable. 

The movement of the gun to the rear as a result of the work 
done upon the gun by the powder gases is known as the recoil, 
and the length of this movement as the length of recoil. 

The return movement of gun to battery after firing is known 
as the counter-recoil, and is equal in amount to the recoil. 

Recoil generally takes place in the direction of the axis of the 
gun, as in Fig. 8. But in special cases where it is necessary to 
clear a deck of a vessel or platform of a car, as in some types of 
railway mounts, the recoil takes place parallel, or slightly inclined, 
to the deck or platform, as in Fig. 9. Occasionally, as in the case 
of anti-aircraft mounts, it is necessary to vary the length of recoil 
to suit the elevation, as in Fig. 10, in order to clear the deck at the 
higher angles of elevation. 


9 


113 


114 


Naval Ordnance 


The type of mounting and recoil represented by Fig. 9 is not 
adapted to the higher angles of elevation, since the recoil serves 
only to reduce the component of the firing force in the direction 
of the recoil. As the angle of elevation increases, the component 
of the firing force acting in the direction of recoil decreases and 
approaches zero as a limit, whereas the component of the firing 
force acting normal to the direction of recoil increases and 
approaches the full breech pressure as a limit. The efifect of this 
is that for angles of elevation approaching 90° the full efifect of 
the breech pressure is transmitted directly to the mount. Mounts 
of this type are built to meet special conditions where the maxi¬ 
mum angle of elevation does not exceed 40°. 

Usually the length of recoil varies with the size of the gun and 
the type of the mount. Mounts of destroyers, and small light 
vessels, have a longer recoil than mounts for battleships and 
battle cruisers, where the deck structure is more substantial and 
capable of sustaining greater forces. 

Where the gun recoils in the mount, the forces acting on the 
mount depend on the resistance offered by the mount to the recoil 
of the gun rather than on the chamber pressure and the diameter 
of the bore. For the same gun and the same powder pressure 
curve, the forces acting on the mount vary inversely as the length 
of recoil. For major caliber guns of battleships, the length of 
recoil is limited to about three calibers on account of the restric¬ 
tions ofifered by the barbette of the turret; for destroyers, where 
the deck structure is light and incapable of sustaining large forces, 
the length of recoil is considerably increased and is usually six 
calibers or more in length. 

As a rule, it will be found there is some limitation on the length 
of recoil imposed by the ship’s structure, and that the determina¬ 
tion of the proper length is compromised by other conditions. In 
the case of turret mounts, an increase of recoil results in a larger 
barbette diameter and greatly increased weights as a consequence. 
In the case of minor caliber guns, longer recoil results in increased 
trunnion heights in order that the breech of the gun shall clear 
the deck at extreme elevation and at maximum recoil. 

After the length of recoil has once been determined to suit the 
practical conditions to be considered in each case, the problem 
with which we are concerned is the absorption of the recoil of the 


Recoil and Recoil Brakes 


ii5 





Fig. 10. 





























Naval Ordnance 


i 16 

moving parts in the most efficient manner. It is obvious that the 
most efficient distribution of forces will exist when the resistance 
to recoil is constant throughout the full length of recoil. 

In all service mountings, the major portion of the energy of 
recoil is absorbed by the hydraulic brake comprising the principal 
part of the recoil system. The counter-recoil system and the fric¬ 
tion of the gun in the slide contribute a small part of the resistance 
to recoil, whereas the gravity component of the recoil weights 
exerts a varying effect as the gun is elevated. 



The advantages of the hydraulic brake can be attributed to the 
large amount of energy that can be absorbed in an unconvertible 
form; to its simplicity and reliability; and to the facility with 
which the resistance offered to the movement of the gun can be 
regulated. The energy absorbed is converted into heat and 
dissipated by the mount into the atmosphere. Springs or com¬ 
pressed air are not suitable for checking the recoil of guns on 
account of the limited amount of energy that can be absorbed, and 
also because the energy absorbed during recoil is returned again 
to the mount during counter-recoil. 

A simple form of hydraulic brake is illustrated in Fig. n. 
This form of brake is used extensively for checking the motion of 
heavy moving parts, and corresponds to the form of brake used 






























































Recoil and Recoil Brakes 


117 

in turret and broadside mounts for checking the return movement 
of the gun to battery in counter-recoil. 

In all forms of the hydraulic brake, including that of the recoil 
system of gun mounts, the brake consists of four simple elements, 
viz., cylinder, piston, liquid and some form of orifice connecting 
the ends of the cylinder each side of the piston. The motion of 
the piston within the cylinder forces the liquid through the orifice 
from one side of the piston to the other. The work required to 
force the liquid through any given orifice can be definitely deter¬ 
mined from the laws of hydraulics and depends upon the area of 
the orifice, the area of the piston, the velocity of the piston, and 
the weight of the liquid. 


counter ■ eecoiu cylinder 



Fig. 12.—Typical Recoil System for Turret Mounts. 


It is obvious that the work done on the piston is equivalent to 
the work done on the liquid. The work done on the piston is 
utilized to overcome the movement of the gun during recoil, 
whereas the work done on the liquid during the same time is 
indicated by a rise of temperature of the liquid. It can be shown 
that the work absorbed by the hydraulic brake can be fully 
accounted for in the rise of temperature of the liquid. Under 
rapid fire conditions, the temperature rise is accumulative from 
shot to shot and results in a considerable rise of temperature which 
must be taken into account in designing the recoil system. 

In the application of the hydraulic brake to gun mounts, the 
recoil cylinder is usually attached to the slide and the piston to the 
gun by means of the piston rod and gun yoke. Fig. 12 shows a 
typical installation for turret mounts. The hydraulic brake is so 



















































Naval Ordnance 


i 18 


proportioned that the total resistance offered by the recoil system, 
counter-recoil system, and friction, with a proper allowance being 
made for gravity forces, is constant and of sufficient magnitude to 
bring the gun to rest in the prescribed distance. With the resist¬ 
ance constant, the velocity of the gun during recoil will vary from 
zero at the beginning to a maximum and back again to zero at 
the termination of recoil. As a result of this varying velocity, 
the area of the orifice will vary for all portions of the recoil, and 
on this account it is necessary to provide means to vary the area 
of the orifice for all positions of the recoil to suit the velocity of 


x 




TYPICAL MINOR CALIBRE RECOIL CYLINDER 

Fig. 13. 



Fig. 14. 


recoil at each point. This is accomplished in various ways as 
illustrated by Figs. 11, 13, and 14. 

In Fig. 11 the diameter of the dash pot is constant and the 
area of the orifice is varied for different points of the stroke by 
varying the diameter of the plunger. 

Fig. 13 shows the usual method of forming the orifice in the 
recoil cylinders of minor caliber gun mounts. A groove of con¬ 
stant depth is cut in the wall of the recoil cylinder, the width of 
the groove varying to suit the velocity of recoil; from two to 
three such grooves are arranged around the inner surface of the 
cylinder in a symmetrical pattern. In case two or more recoil 























































Recoil and Recoil Brakes 


i 19 

cylinders are used, the arrangement of grooves in all cylinders is 
similar and the cylinders are interconnected to equalize the pres¬ 
sure in all cylinders. 

Fig. 14 illustrates the usual method of varying the orifices in 
turret mounts. Two or three rods are passed through apertures 
in the piston; the rods are attached to the ends of the recoil 
cylinders as shown. By varying the diameter of the rods, the 
proper variation in the area of the orifice for all points of the 
recoil may be obtained. 

127 . The principles controlling the action of the hydraulic 
brake.—The principles controlling the action of the hydraulic 
brake are simple and may be understood from the analysis of the 
hydraulic brake illustrated in Fig. n. The following symbols 
will be used, all units being expressed in terms of pounds, feet 
and seconds: 

W r — Weight of the moving parts (plunger) in pounds. 

A/ r = The mass of the moving parts = 

R cr = The total resistance in pounds offered to the move¬ 
ment of the plunger. 

V cr — Velocity of the plunger at any time t. 

V cr 0 — The maximum velocity in feet per second of the 
plunger at the time the plunger enters the dash 
pot. 

V1 r — Velocity in feet per second of the liquid through the 
orifice at any time t. 

y = The weight of a cubic foot of liquid in the dash pot. 
(76 pounds for usual naval liquid, 80 per cent 
glycerine and 20 per cent water.) 

g = Acceleration of gravity = 32.16. 

Ay — The effective area of the plunger in square feet. 
a,. = The area of the orifice in square feet at any time t. 

5 cri =:The full stroke of the buffer in feet. 

S cr = The stroke of the buffer corresponding to velocity 

V r . 

a = Negative acceleration (or retardation). 

In Fig. 11 the velocity of the plunger upon entering the dash 
pot is expressed by the letter V C r 0 , and the weight of the moving 



120 


Naval Ordnance 


mass of the plunger, and the parts to which it is attached, by W n 
in which case the energy of the moving mass is 

_ W r f 7 Arp 

As the plunger enters the dash pot, the liquid escapes through 
the orifice formed by the plunger and dash pot, in the direction 
indicated by the arrows. 

The resistance set up by the liquid as it escapes through the 
orifice acts on the end of the plunger. The amount of resistance 
exerted depends on the area and velocity of the plunger; the area 
of the orifice through which the liquid escapes; and the weight of 
the liquid. The area of the orifice may be varied throughout the 
stroke of the plunger by giving the proper form to the plunger. 
It is customary to vary the area of the orifice so that the resistance 
offered to the motion of the plunger will be constant throughout 
the stroke; in which case the work of resistance opposing the 
motion of the plunger may be expressed 

Work of resistance = i? cr 5 , cri . (2) 


The value of the resistance R cr must be of sufficient magnitude 
to bring the plunger to rest in the distance Ncn, in which case we 
may write 


RcrSc 


W r V 2 


or 1 


cr 0 


2 o’ 


(3) 


From equation (3), the value of the resistance R cr necessary to 
bring the plunger to rest in the distance Sen is 


Rcr — 


IVrV 2 ere ^ 

2 gS cri 


( 4 ) 


The volume of liquid that passes through the orifice is the 
volume of liquid displaced by the piston. We therefore have at 
any instant 

V crAr—V irOr- 


Or, for the velocity of flow 


V ir = 


V crA r 

Ctf 


( 5 ) 


From Torricelli’s law, for the flow of liquid through an orifice, 
we know that the pressure required to produce this velocity of 


1 






Recoil and Recoil Brakes 


I 2 I 


flow is the pressure due to a column of liquid whose height in 
feet is given by the equation 

V\r = 2gh. (6) 


Substituting in equation (6) the value of V ir from equation 
(5) and solving for h, we obtain 


h = 


V 2 crA r 2 

2ga,- 2 


(7) 


The weight of a cubic foot of liquid being y, the weight of the 
column whose area of cross-section is one square foot will be yh. 
And the weight of the column whose area of cross-section is equal 
to that of the plunger will be A r yh. Therefore, A r yh is the pres¬ 
sure on the piston. Substituting in this expression the value of li 
from equation (7), we have, for the total pressure on the piston, 
for any velocity V cr 



A r 3 V 2 cr 

2 ga r 2 


( 8 ) 


This equation is general; and expresses the relationship between 
R ir , A r and a r , for any given velocity of the plunger. 

Solving for a,- 2 , we obtain 


(9) 


„ 2 _ yASV'cr 

Ur —- 75 -'• 

2gR C r 

From equation (9) it will be seen that the area of the orifice 
may be determined for any portion of the stroke of the plunger, 
if the pressure R cr and velocity of the plunger at that point are 
known. 

To determine the velocity of the plunger, we know that when 
the total resistance to the movement of the plunger is constant 
the retardation is constant; and we may express the relationship 
between velocity, space and retardation by the expression 

V 2 cr — 2aS cr- ( IO) 


By substituting in this expression the known values of V cr and 
S cr at the point where the plunger enters the dash pot, we may 
determine the value of the retardation constant, for the particular 
buffer under consideration. Substituting the value for retardation 
thus obtained for a in equation (10), and treating V cr and S cr 
as variables, we may obtain the value of the velocity for all points 
of the stroke. It will be observed from equation (10) that the 




122 


Naval Ordnance 


velocity curve is a parabola with its origin located at the bottom 
of the dash pot. (See Fig. 4.) 

By substituting the value of V cr in each case, in equation (9), 
the area of the orifice for all points of the bufifer may be obtained. 

Equation (9) makes no allowance for the friction of the liquid 
and the contraction of the liquid vein as it emerges from the dash 
pot. This is provided for in actual practice by adding from 15 
per cent to 30 per cent to the area of the orifice computed by 
equation (9). The particular factor applying in each case depends 
on the shape of the orifice formed between the dash pot and the 
end of the plunger, the larger factor being used where the corner 
of the plunger is square, and the smaller factor where a radius is 
formed on the end of the plunger. Intermediate factors are used 
which depend on the shape of the orifice. 

The liquid used in the dash pots and recoil cylinders of the navy 
is composed of a solution of 80 per cent glycerine and 20 per 
cent water, which weighs about 76 pounds per cubic foot. This 
liquid has a low freezing point and fairly constant viscosity within 
the ordinary temperature ranges, and has given satisfactory re¬ 
sults in naval mounts for a great many years. Certain grades of 
bufifer oil of the same weight give equally good results. 

Equation (9) can be used for computing the area of orifice of 
any form of hydraulic brake when all the circumstances regarding 
velocity of retarded recoil and variations in pressure are known 
for all points of the stroke. 

The proper allowances for all forces acting on the gun can be 
made easily after all other circumstances of recoil due to the 
action of the powder gases are determined. The effect of the 
powder gases on the recoil motion of the gun may be determined 
in the following manner : 

128 . Velocity of free recoil.—Since the proper allowance can 
be made for the elevation of the gun and action of gravity and 
other forces after the other factors are determined, it is first 
assumed that the gun is mounted in a horizontal position and is 
acted on by the pressure of the powder gases unopposed by fric¬ 
tion or brake. The parts of the system acted on by the powder 
gases are the gun, the projectile, and the powder charge [includ¬ 
ing the burned and unburned portions of the charge at any instant]. 
The curve of velocity of free recoil of the gun during the time of 


Recoil and Recoil Brakes 


123 


the discharge of the projectile will be similar to the curve of 
velocities for the projectile and powder gases during the same 
time, except to a reduced scale on account of the differences in 
masses. From the momentum of the projectile and powder gases, 
the momentum of the gun may be determined. Since the mo¬ 
mentum of the gun at any time is equal to the sum of the 
momentum of the projectile and powder gases, we may write 

MrVf = mVp + mV c . (11) 

M r , m, and m representing the masses of the gun, projectile and 
powder charge, respectively; and Vf, V v , and V c the velocity of 
these masses. 

The velocity of the projectile at any point in the bore of the 
gun, expressed as a function of the travel of the projectile in the 
bore, is determined from equations on Interior Ballistics (Chapter 
III). These equations assume that the velocity-space curve of the 
projectile in the bore is a hyperbola, 


V P = 


au 

b + u’ 


(12) 


NOTCi-THE CURVES BELOW WERE LAID DOWN FOR A 16-INCH MOUNT. THE 
CURVES WILL VARY To SUIT EACH TYPE AND CALIBER OF MOUNT. 





















Gfi 

se: 

s 

:ei 

ISE 

T 


iC7 












4; 




20, 

L 

F* 0 

E& 

lES 


yz 






tv 

H 

n 


f 

1A 

c. P 

0\N 

( 

DE 

R 

PR 1 

'S: 


•42 






















\ 

AS 































X. ( 

>ov 

/D€ 

R 

PR 

ES 

»UI 

IE 






































_ 




O I 2 3 4 6 7 ft 9 10 II 12 13 I* IS 1 C 17 16 19 20 21 22 23 24 25 26 27 28 


NO. 

DESIGNATION 

OF CURVES 

HORIZONTAL. 

SCALE. 

vc rtical 
SCALE 

1 

VELOCITY 

Of PROJECTILE 

FUNCTION OF SPACE 

ID'VISlONx 2 FT 

1 DtVlSlON - 5 OOF. 5 

2 

VELOCITY 

OF PROJECTILE 

FUNCTION or TIME 

IDIVISION'?Oo4SK 

IDNISION= 500F.S. 

3 

VELOCITY 

OF FREE RECOILIRECOILING PARTS! FUNCTION OF TIME 

IDIV1 SION c7oo4 SC C 

IDNIS10N-.SO84F S. 


Fig. 15. 


where a and b are parameters determined by equations (13) and 
(i4)- 

V p = Velocity of projectile at any point in the bore in feet per 
second. 

a = 6823A*0f)\ (13) 

A = Density of loading (varies from .4 to .7). 
w — Weight of charge in pounds. 
p — Weight of projectile in pounds. 




























































124 


Naval Ordnance 


By transposing equation (12) and substituting the total travel 
for u and the corresponding velocity at the muzzle V Pl for V p , 
we get the parameter b in feet: 

b=™i- u . (14) 

' Pi 

The velocity of the center of mass of the powder charge is 
unknown. It is obvious, however, that if the charge were in¬ 
stantaneously converted into gases the mean velocity would be 
one-half the algebraic sum of the velocities of the gun and the 
projectile. Assuming this to be true, and also that the velocity 
of the breech at the instant the shell leaves the muzzle is zero, we 

may without great error substitute in equation (n)-^for V c - 
Making this substitution and replacing masses by weights, we have 

WrV f -(p + .sW)V p = o. (15) 

Multiplying equation (15) by time, (/), and substituting Sf 
for Vft and u for V p t, we may write 

WrS f -(p + .slV)u = o, (16) 

where Sf is the space travelled in free recoil, and W is the travel 
of the projectile. 

Substituting the value of V p from equation (12) in equation 
(15) and transposing, 


v _ (/> + • 5 W) 

f ~ W r 

an 

b + u ’ 

(i 7 ) 

y s _(/> + • 5 ^) 
fl ~ W r 

V vi , 

(18) 


Vf! being the velocity of free recoil when the projectile leaves the 
muzzle. 

From equation (16), we have 


—wr 


u. 


(19) 


At time t ly u is equal to u t . We may, therefore, express the 
space passed over by the recoiling parts at the time t x , the time 
when the projectile reaches the muzzle, by the following equation : 

c. _ (/>+■ $w) 








Recoil and Recoil Brakes 


125 


The value Vf lt equation (18), is not the maximum velocity of 
free recoil, since sufficient pressure still exists in the gun for a 
short time after the shell leaves the muzzle to further increase the 
velocity of free recoil of the gun. 

The time the gases continue to act after the projectile leaves 
the muzzle, and the maximum velocity attained by these gases, are 
not definitely known. Measurements taken by a Severt veloci- 
meter, however, indicate that for the usual muzzle velocities [i. e., 



NOTE : M.RP DENOTES POINTS OF MAXIMUM POWDER. PRESSURE. 

PL.M. DENOTES POINTS WHERE PROJECTILE LEAVES MUZZLE 


NO 

designation of CURVES 

"U<5FizftNT/M_ - 

SCALE 

VERTICAL 

1 

VELOCITY OF FEES RECOIL (ALL RECOILING PARTS) FUNCTION OF TIME 

1 DIVISION • oftw SEC 

1 DIVISIONS 3F.S, 

z 

•ETA.ROA.TlON OF ALL RECOILING PARTS FUNCTION OF TIME 

1 DIVISION * 0^01 sec 

1 DIVISION = 3 PS 

? 

velocity 0 * retarded recoil (recoiuno parts) function op tims 

ioivision=o)oi sec 

1 DIVISION » 3 P *. 


VELOCITY OF RETARDED RECOIL (RBCOlLINO PARTS) FUNCTION OF SPACE 

1 DIVISION » 2lb 

1 DIVISION ■ 3 F.S. 


NOTE: THE ABOVE CURVES WERE LAID DOWN FOR A 16-INCH MOUNT. THE CURVES 
WILL VARV TO 6UIT EACH TYPE AND CALIBER OF MOUNT. 

Fig. 16. 


from 2100 foot-seconds to 3150 foot-seconds] the correct values of 
the maximum velocity of free recoil may be obtained from equa¬ 
tion (18) by substituting for one-half WV v the value 4700 xlV, 
in which case we may write, for the maximum velocity of free 
recoil (V f3 ), 


ts _pV p + 4jooW 

f3 ~ Wr 


(21) 


It should be noted that the coefficient 4700 applies only to smoke¬ 
less powder for the velocities mentioned. (Note. —For black 
powders, 3000 should be used for corresponding velocities.) Also 






















































































126 


Naval Ordnance 


that equation (21) applies only in the case of free recoil and does 
not express the velocity of retarded recoil. It is necessary that we 
know the velocity of retarded recoil at all points of the recoil in 
order to determine by means of equation (9) the correct form of 
the orifice to be provided at all points to bring the gun to rest in 
the desired distance. 

The velocities for retarded recoil will be determined in a manner 
hereinafter described. 

129. Computation of velocity of retarded recoil. —The various 
steps necessary to determine the velocity of retarded recoil in 
order that we may compute the area of the throttling orifice by 
equation (9) are as follows: 

1st. Compute the curve of velocities of the projectile in the 
bore function of space. (See Curve No. 1, Fig. 15.) 

2d. Compute the curve of velocities of the projectile function 
of time. (See Curve No. 2, Fig. 15.) 

3d. Compute the curve of velocities of free recoil of recoiling 
parts function of time. (See Curve No. 1, Fig. 16.) 

4th. Compute the curve of retardation function of time. 
(See Curve No. 2, Fig. 16.) 

5th. Compute the curve of velocities of retarded recoil func¬ 
tion of time. (See Curve No. 3, Fig. 16.) 

6th. Compute the velocity of retarded recoil function of space. 
(See Curve No. 4, Fig. 16.) 

Having determined the velocities of retarded recoil, function of 
space, equation (9) may be used for computing the area of the 
throttling orifice for all positions of the recoil when the brake 
force, counter-recoil force, gravity force, and- friction force for 
each part of the recoil are known. 

Velocity of projectile—function of space. —Equation (12) 
gives the velocities of the projectile in the bore, function of space 
(travel of projectile). 

Velocity of projectile—function of time. —To determine the 
time of travel of the projectile in the bore from equation (12), 
we may substitute the values of 


an 
b + u 


for V 


in the following equation which expresses the relation between 
time, velocity, and space when the velocity is variable, 



Recoil and Recoil Brakes 


127 


dt = 


du 

V ’ 


or, substituting for V, 


b + u 


dt = 


du 
au 
b -b u 


Transposing and integrating, 

fo±o du . 


t = 

t- 


au 


f bdn 
J au 


+ 


~ud u 
au 


t = 


a 


du 1 
0 u a 


du. 


b , u 

t = — loge u H-b constant c. 

a a 


(22) 


(23) 


(23-O 

(23-2) 

(23-3) 

(23-4) 


When u is equal to o, t is equal to o, and log c u is equal to 
infinity, and we cannot determine the constant of integration (c) 
without imposing an assumed condition. 

It is reasonable to assume that for extremely small values of u 
the time will be approximately the same, whether the velocity- 
space curve is a hyperbola or a parabola. 

It has been found from investigation that when the value of u 


is equal to , the time equations for the two curves could be 

equated and the constant of integration for equation (23-4) 
determined with considerable accuracy. 

Assuming the velocity curve, function of space, is a parabola, 
we may write 

Vp=V2pU. (24) 


Substituting the value of V p from equation (24) in equation (22) 
[which expresses the relation between time, velocity and space, 
when the velocity is variable], we have 


dt = 


du 

V 2 pll 


(24-1) 
















128 


Naval Ordnance 


Transposing and integrating, 

t = 

from equation (24) 

V^p = 


yur^du 

2«i 

(24-2) 

J V 2 p 

V 2 p ’ 

Vv 

V w 


(24-3) 

2 p from 

equation (24-3) 

in equation 


(24-2), we have 


t = 


2U- 

JZ 

v« 


2 -u 

TZ 


(24-4) 


The time for the parabola up to the point where u — is 


211 

t= T -y- — 2 X 


since 


T/ — au 

p ~ b + h 


h IOI 


IOO 


a 


ab 100 

IOO IOlfr 


20 2b „ b 

- = 2.02 — 

100a a 


a 


(25) 


101 


The time for the hyperbola up to the point where 11 is equal 


to 


IOO 


is 


, b , b . b 

t— — log e -h -— 

a 100 1000 


+ c. 


(25-O 


Equating the values of t given by equations (25) and (25-1) 
and solving for c, we have 

b b 


b b 1 

c — 2.02 — — — log e 

a a 100 


1000 


_ ± 
a 


2.02 - log e 


IOO 


— .01 


(25-2) 

(25-3) 


Substituting the value of c given by equation (25-3) in equa¬ 
tion (23-4) and simplifying, we have 


ti b 

t= —-4-[loge ll ~ loge .01 & 4-2.0l], 

a a 


(25-4) 


Equation (25-4) expresses the time for all positions of the 
projectile in the bore, where u represents the travel, t the corre¬ 
sponding time, and a and b the parameters of the hyperbola deter¬ 
mined from equations (13) and (14). 



















Recoil and Recoil Brakes 


129 


To determine the time at which the projectile reaches the muzzle 
from equation (25-4), where the time is represented by t u and 
the travel to the muzzle by u lf we have 


t Ui 

a a 


locr, 


te« 


lo 


tee IOO 


+ 2.01 


( 25 - 5 ) 


From equation (12) the velocity-space curve of the projectile 
may be determined. This curve is represented by Curve No. 1, 
Fig. 15, and from equations (12) and (25-4) the velocity-time 
curve of the projectile may be determined up to the time the pro¬ 
jectile leaves the muzzle (see Curve No. 2, Fig. 15). 

Velocity of free recoil.—Function of time. —Curve No. 2, Fig. 
15, also represents the velocity of free recoil of the gun to a 
reduced scale. Curve No. 3 of Fig. 15 coinciding exactly with 
Curve No. 2 of Fig. 15, the ordinates of Curve No. 3 represent 
lower velocities on account of the greater mass. The ratio of the 
two scales are inversely proportional to the mass of the gun and 
the masses of the projectile and half the powder charge. 

As stated before, sufficient pressure exists in the bore for a 
short time after the shell leaves the muzzle to further increase the 
energy of recoil of the gun. To determine the time after the 
projectile leaves the muzzle, it is assumed that the reaction on the 
gun falls ofif proportionally to the time, that is, 

P b = P bl -K(t-t 1 ), (26) 


where Po is the total reaction of the powder gases on the recoiling 
parts, at any time between t 1 and t 3 , and Pb x is the reaction at the 
time t l when the projectile leaves the muzzle—the value of 
in equation (26) being determined from the following equation: 


f„= "gf •' (26-D 

g(b+u,y 

Note.— Equation (26-1) is derived from Le Due’s formula for the deter¬ 
mination of the pressure curve in the bore, where 


Pbi is the total pressure in lbs. in the bore when the projectile is at the 
muzzle. 

Mi is the travel of projectile to muzzle in feet. 
p is the weight of the projectile in lbs. 

a and b are parameters determined from equations (13) and (14). 

K is a constant to be determined. From (26) 


K = 


Pbi-Pi, 


10 


(26-2) 








130 


Naval Ordnance 


Substituting in this equation the time t 3 that the powder gases 
cease to act, we have 

(27) 

t s t 1 

since Pi, is zero when t = t 3 . 

Substituting the value of K from equation (27) in (26), we 
have 

P b =P H ~ (*“*i)* (28) 

From equation (28), the effect of the powder gases can he 
determined for any time after the projectile leaves the muzzle. 

The momentum imparted to the recoiling parts by the powder 
gases during an increment of time dt after the projectile leaves 
the muzzle is 

M r dV = Phdt, (29) 


where M r is the mass of the recoiling parts. 

Substituting the value of Pb equation (28) in equation (29) and 
transposing, 

' dl /— P Pt\dt _ Pb x tdt (29-1) 

)v n Mr MrU:~t 1 ) 

In the above equation, Vf 1 is the velocity of free recoil at the 
time (t,) when the projectile leaves the muzzle, obtained from 
equation (18), and V f 3 is the maximum velocity of free recoil at 
the time ( t .,) when the gases cease to act | obtained from equation 

( 2 I )I- 

Integrating (29-1) between the limits of Vf and Vfx and the 
corresponding time t and we may determine the velocity of free 
recoil for any time ( t ) between t 1 and t 3 . 

t _ P H t 2 

M.. 


v 

v, 


f 

V 

t r 

ft 


h - 


2M r (t 3 — t 1 ) 


T7 v Pin(t-tnY 

Vf ~ VH ~~M r 2 MriU-Kf 


Transposing and simplifying, 


V t = V fl + 


p bl (t-t x ) 
Mr 


_ (f-Q I 

2 (t 3 — t 1 ). 


(29-2) 


(29-3) 


Substituting in equation (29-3) the value of t 3 for t, and its 
corresponding velocity Vf 3 for Vf, we have 


Vf,= V f x + 


Pinih-h) r t _ (/,-/,) 


M r 


2(/ a -/i)J 


(29-4) 



















Recoil and Recoil Brakes 


131 


Simplifying, 


From which, 


, , 2 M,(V„-V n ) 

1 3 — ‘ 1 ' D » 


( 29 - 5 ) 


( 29 - 6 ) 


where t 3 is the time when the gases cease to act. 

The value Pi 1 in equation (29-6) may be obtained from equa¬ 
tion (26-1). 

The curve of velocity of free recoil of the recoiling parts as 
a function of time, while the projectile is in the bore, may be 
determined from equation (12) by multiplying the velocity V p of 
the projectile in the bore for any position of travel u by the 


ratio 


IVr 

P + .5W 


or 



au 

b + n 


X 


lV r 

P + -5W* 


( 30 ) 


The time for any position u of travel of projectile in the bore 
may be determined from equation (25-4). 

The velocity of free recoil of the recoiling parts as a function 
of time after the projectile leaves the bore may be determined 
from equation (29-3). (See Curve No. 1, Fig. 16.) 

130 . Velocities of retarded recoil.—Function of time.—We 
have, so far, dealt only with the velocity and time of free recoil. 

After the time when the free velocity of recoil attains its 
maximum value V / 3 , the gun will continue to recoil indefinitely at 
the velocity Vf 3 if no restraining force is applied, in which case, 
the curve beyond this point would continue parallel to the axis 
o t 4 , as shown in Fig. 16. 

In practice, however, the velocities of free recoil are never 
reached, since they are continuously reduced under the action of 
the restraining forces, until the gun is brought to rest at the end 
of recoil. The restraining forces consist of the hydraulic brake 
force, the counter-recoil forces, friction, etc. The sum of these 
forces is the total resistance to recoil R r , which must be offered to 
the recoil of the gun to bring it to rest in the required distance. 

Since the total resistance to recoil is constant, the retardation 
will be constant and we may represent the curve of retardation by 







132 


Naval Ordnance 


a straight line drawn from the origin of motion so that the 
retardation (negative acceleration) will be 



(30 


the ordinates of the line representing negative velocities and the 
abscissae corresponding times. (See Curve No. 2, Fig. 16.) 

Note.— Since the ordinates of the line oC represent negative velocities, 
the line properly belongs below the axis. For convenience, however, the 
line is drawn above the axis as shown in Fig. 16. 


Since the resistance R r is constant, the retardation is constant, 
and we may write 


Rr = aM r , 


( 31-0 


that is, the retardation is the product of retardation and mass of 
the recoiling parts, from which 



The tangent of the angle f 4 oC is equal to —a or to- -jj . 

The length of recoil of the mount, having been previously 
determined by practical considerations of the, design, the problem 
is to determine the value of the total resistance R r that will check 
the recoil of the gun in the required distance. 

We will proceed to the determination of the resistance R r in 
the following manner: 

Curve No. 1, Fig. 16, represents the velocity of free recoil, 
function of time. 

We have seen that the tangent to the curve at any point repre¬ 
sents the acceleration at that point. We have also seen that the 
negative velocities due to the constant resistance R r can be repre¬ 
sented by the straight line oC, Fig. 16. 

It is obvious that the maximum negative velocity due to the 
resistance must equal the maximum velocity of free recoil, since 
at the end of recoil 

Vfi-Vn (max.)=o, (32) 

where V n is the negative velocity due to the retardation and V n 


Recoil and Recoil Brakes 


133 


(max.) is the maximum value at the end of recoil obtained from 
the expression 

V „(max.) = —at 4 (33) 


where t i is the time of retarded recoil. 

From equations (32) and (33), we may write 

Vfz — at 4 , (33-0 

and from equation (33-1) and the value of -a=^ r . From 
equation (31-2), we have 

from which 


V f t 
Vh M/ 4 ’ 


R r= KhMlL, 


(34) 

(35) 


Since M r is known and V f 3 can be determined from equation 
(21), the value of the resistance R r may be determined if the 
time of retarded recoil is known. 

It is obvious that the velocity of retarded recoil ( V r ) at any 
time is the difference between the velocity of free recoil and the 
negative velocity resulting from the retardation force at the 
corresponding time, or 

Vr=V f3 -V n . (36) 


From equation (36) the ordinates of the curve of retarded 
recoil may be obtained (see Curve No. 3, Fig. 16) if the values 
of V n are known. The values can easily be determined after tbe 
value of R r is determined and the slope of the retardation line oC 
ascertained. 

Velocity of retarded recoil.—Function of space.—Since an 
increment of space is equal to the time increment of velocity, we 
may write 

dSr=Vrdt, (37) 

from which 

Sr=\V r dt, ( 37-0 

where S r is the length of retarded recoil corresponding to the 
velocity V r . 

From equation (37-1) it will be seen that the area under the 
curve of retarded velocities (Curve No. 3, Fig. 16), between the 



134 


Naval Ordnance 


origin and the ordinate corresponding to the velocity V r , will rep¬ 
resent the length of recoil corresponding to the velocity repre¬ 
sented by the ordinate, and the total area under the whole curve 
will be the length of recoil S, 4 - 

The area under the curve of velocities of free recoil (Curve No. 
i, Fig. 16) will, for the same reason, represent the distance 
traveled in free recoil. The area under the curve from the origin 
to point Vf z will represent the distance traveled in free recoil Sf 3 . 

From Fig. 16, it will be seen that the area under the curve of 
velocities of free recoil (Curve No. i, Fig. 16) includes all the 
values of free recoil up to time t 4 . The area under the triangle 


t 4 oC can be indicated by , which is the reduction of travel 

of the recoiling parts due to the constant retarding force R r . 

Since the area under the curve of retarded recoil is S,- 4 , we may 
write for the length of recoil 


Sr. = S„+V ls (t,-t x )-^, 

simplifying 

Sr. = S„ + !^- 

from which 

f — 2(Sr 4 —Sf s +V f-J z ) 

Vf 3 


(38) 

(39) 


Substituting the value of t 4 , equation (39) in equation (35), we 
have for the value of R r , 

MrV'f 3 


Rr = 


(40) 


2(Sr 4 + V f 3 t 3 — Sf 3 ) 

Vf 3 in the above equation is the maximum velocity of free recoil 
determined from equation (21) ; S,- 4 is the length of recoil in feet; 
t 3 is the time the gases cease to act, determined from equation 
(29-6) ; and N/ 3 is the space recoiled by the recoiling parts when 
the gases cease to act. S f . f may be determined in the following 
manner: 


Since ds = Vfdt 




cis = 


and from (29-1) 


I s fl 


V fdt. 


(40 


V,= 




/V 2 




Vf 


(42) 










Recoil and Recoil Brakes 


135 


Substituting equation (42) in equation (41), 


! $ r 


ds — 


Pb X tdt 

1 Mr 


P\ n t~dt 


2 


+ V f A dt. 


(43) 


Integrating and transposing. 


Sf — Sf 1 + 


2M r 






(43-0 


Sf being the space of free recoil corresponding to time t between 
the values S fl and Sfo. 

Substituting Sf 3 for Sf and t 3 for t in equation (43-1), and 
simplifying, 


Sfz — Sfi + (t. 5 


*,) ^x + 


3 ^r - 


( 43 - 2 ) 


With the value of Sf 3 given by equation (43-2), the value of 
the constant resistance R r given in equation (40) may be deter¬ 
mined. 

Having the value of R r , the slope of the line oC may be deter¬ 


mined from the relation —a- 


n 

where is the tangent of the 


angle of the slope. 

The curve for velocity of retarded recoil, function of space, can 
be computed in the following manner: 

Since the retarding force R r is constant, the retarded velocity 
■ V r at any point will be 


V r = V f — V n 


(44) 


where V„ is the reduction in velocity due to R r . 

/v* R t 

Also V n ——at, but since from which 

Vr=v ’~ir/ (44_I) 

Equation (44-1) may be solved for the various values of time 
and the space (S’, ) traveled for corresponding times computed as 
follows: 

Let S n represent the reduction in space traveled at any time due 
to R r . [Where S H represents the space traveled by the recoiling 
parts at any time t, starting from zero velocity with no forces 
except R r acting.] 


I 


/ 









136 


Naval Ordnance 


Then 


9 — 1 „* 2 —1_»- t 
0 n 2 a< * 


Also 


From which, substituting f 4 )f-t 2 for S n , 


Sr — Sf — Sn. 

Rf 

Mr 


Sr = Sf 


1 R-r 


( 45 ) 


(45-0 


(45-2) 


Equations (44-1) and (45-2) may be solved for the full recoil, 
but it is more convenient to use the following method after pass¬ 
ing the point of maximum velocity of retarded recoil: 

Since the inertia force is the only force acting to produce recoil 
after the maximum velocity of free recoil is attained, we may write 

MlpL = R r (S ri -Sr), ( 46 ) 

from which 


T/ _ 2 Rr(Sr 4 -Sr) 

Mr 


( 46-0 


Point of maximum velocity of retarded recoil.—It is often 

necessary in the early stages of the design to know the maximum 
area of the throttling orifice in order to properly proportion the 
various parts of the recoil system. The maximum area of 
throttling orifice will coincide with the point of maximum velocity 
of retarded recoil, and the maximum area may easily be deter¬ 
mined from equation (9) when the maximum velocity of retarded 
recoil has been determined. The point of maximum velocity of 
retarded recoil may be determined in the following manner: 

For the point corresponding to the maximum velocity of re¬ 
tarded recoil, let t 2 represent the time, V f 2 the velocity of free 
recoil, Sf 2 the space traveled in free recoil. At the point of 
maximum velocity of retarded recoil, P& equals R r , since at this 
point the tangent to the curve of velocity of retarded recoil is 
parallel to the X-axis and the accelerating and retarding forces 
are equal. 

Substituting R r for P b in equation (28) and solving for (t — t^ 
at the point t 2 , we have 


( / 2 _ f 1 ) — ( Pb 1 ~ Rr) (^3 ~ fj) . 

p 61 


(47) 


transposing equation (47), we get 


p b ^ — (Pbi~Rr) * 


t 2 t x 


(47-0 






Recoil and Recoil Brakes 


137 


Substituting in equation (29-3) the value of Pi n from equation 
(47-1), and writing t 2 for t and Vf 2 for Vf, we get 


77 _ 77 1 (P&i — Rr) (t 3 —t x ) (t 2 —t t ) 


(h-u) ' 

2 (G ^1 )- 


( 48 ) 


Substituting value of t 2 — t 1 , from equation (47) in equation 
(48), we have 


77 —17 4- (-^bi — Pr) (t 3 — t, ) 

Mr 

77 — 77 I (Rfti — Pr) (t 3 ~t 1 ) 

V f 2— P All iTf 


(P bl -p,.)(t 3 -t t ) 
2P&1 (^ 3 ~ h ) 


]> ( 48 - 1 ) 


(P 6l -P r ) l 

2 P b] J 


( 48 - 2 ) 


being the point in the velocity of free recoil curve corre¬ 
sponding to the maximum velocity of retarded recoil. 

Substituting the value of (t 2 — t 1 ) from equation (47) in equa¬ 
tion (43-1), giving Sf its value Sf 2 , we get 


C _ C I 77 (Pbi — Pr) (G ^ 1 ) . Rr)~(t s 1 1 )~ 

r2_ ; 1 + P bl 2M r P 6l 


+ 


P bl (P bl -P r ) 3 (t 3 -^) ! 

6 M r p hx *(t 2 -t 1 y 


(49) 


or 


C _C I (P&1 P*0 (G ^ 1 ) 77. 4_ (P&1 ^r)(t 3 — ty) 

*f*-*f* + P H 2 Mr 

(P &1 -Pr) 2 (t 3 -f 1 ) 

6M r Pbi 


(49-0 


5 V 2 being the space traveled in recoil when the maximum velocity 
of retarded recoil occurs. 

131. Determination of area of throttling orifice.—Having 
determined the curve of velocities of retarded recoil, we may deter¬ 
mine the area of the throttling orifice at all points of the recoil to 
give the required hydraulic resistance from equation (9). 

The constant resistance R r includes the hydraulic brake resist¬ 
ance, the resistance offered by the counter-recoil system, fric¬ 
tional resistances, etc. Gravity also exerts a varying effect, 
depending on the angle of elevation of the gun. The proper 
allowance must he made for the forces mentioned and the proper 
adjustments made in the value of the hydraulic brake resistance 
in order that the total resistance, i. e., the algebraic sum of the 
resistances, shall be constant for all points of the recoil. 



















Naval Ordnance 


138 


The equation of forces may be written as follows: 

R r = Wrf cos i// — IV r sin 1 p + Rh + R s + Rp- ( 5 °) 

Where 

W r — The recoiling weight in pounds. 

/ = Coefficient of friction. 
ip = Angle of elevation. 

R s =: Counter-recoil force in pounds at any point. 

R h = Hydraulic brake resistance at any point. 

R p = Packing gland resistance. 

From equation (50) the value of the hydraulic brake resistance 
at any point may be computed, or 


R h = R r — IV r f cos ip + W r sin ip — R g — R p . (51) 

Substituting the proper value of Rh and V r for each point of 
the recoil in equation (9), we have for the area of the orifice at 
any point 


Or — 


C-YAVVV 

2gRh 


( 52 ) 


Where a, is the area of the orifice in square feet. 

¥ is the weight per cubic foot of the recoil fluid. 

V, is the velocity of retarded recoil in feet per second. 
g is the acceleration of gravity 32.16. 

Rh is the hydraulic brake resistance in pounds for any 
point corresponding to the velocity V r . 

C is a variable coefficient of contraction which varies 
between the limits of 1.15 to 1.37 for throttling rods 
[such as are used in major caliber mounts], and 
between 1.12 to 1.20 for grooves [such as are used 
in minor caliber mounts]. 


It should be noted in the case where n orifices are used, the area 

A 

for each orifice is equal to —where a r is the total area of orifice 

n 

determined from equation (52). 

Fig. 17 shows the curves for recoil areas for a throttling rod 
type of recoil system. The required area of orifice in square 
inches for each point of the recoil is represented by the ordinates 
of the curve for each point of the recoil. (See Curve No. 2, Fig. 
17.) Curve No. 1, Fig. 17, shows the curve of areas where the 



Recoil and Recoil Brakes 


139 


factor C has the constant value 1.15. Curve No. 2, Fig'. 17, is 
laid out with C equal to 1.15 at the origin and increasing to 1.37 
at the maximum ordinate. It will be noted that there is a space 
of about 2\ inches where the maximum ordinate remains constant. 
This space is equal to the length of the piston, and represents the 
point at which the throttling edge of the orifice shifts from the 
forward edge of the piston to the rear edge. 

From Curve No. 2, Fig. 17, the actual diameters of the recoil 
rod at the various positions of recoil are determined. 



NO. DESIGNATION OP CURVES 

» CURVE ORDINATE S «U5 X COMPUTED AREA|lOrvTsiOM=ZSQJH]lD(V«IOH^2fO 

t CURVE ORDINATES » K * COMPUTED AREA I WVtSlOWZSfrM ICHViaiOI-Zlb 


VERTICAL HORIZONTAL 
SCALE_SCALE 


NOTE.’ K VARIES PROM 1.15 TO 1.37 TO SUIT ORIFICE AS SWOWM . 


CorwajkI 

POSITION 
OF PISTON 


Pl 8TON 
AT MAXIMUM 
RECOIL VELOCITY 


1 


REAR 
POSITION 
OF PISTON 


NOTE: THE ABOVE CURVES WERE LAID DOWN POK A 16-INCH MOUNT THE CUBVES 
WILL VABV TO SUIT EACH TVPE AND CALIBER OF MOUNT. 

Fig. 17. 

RESISTANCE IN lbs. 



132. Work of resistance. —The work of resistance to recoil and 
the manner in which the values of the elements of resistance vary 
throughout the length of recoil may best be represented graphic¬ 
ally by the work diagram shown in Fig. 18. The line OC in the 












































































































Izj£> 


Naval Ordnance 


diagram represents the length of recoil; the constant retarding 
force which is the total resistance R r offered to recoil is repre¬ 
sented by the ordinate OH. 

The value of the resistance R r is a maximum when the gun is 
fired at the maximum angle of elevation, since the value of 
IV r sin i p, equation (50), is maximum at that angle. On this 
account, the value of the resistance R r is computed from equation 
(50) for the maximum angle of elevation. OH in Fig. 18 repre¬ 
sents the value of R r thus computed. 

Referring to Fig. 18, the area of the figure ODEC represents 
the work of recoil with the gun fired horizontal; the area DHJE 
represents the work of gravity at the maximum angle of elevation, 
where the ordinate DH — EJ represents the value W r sin ip (equa¬ 
tion (50)). The area FHJG represents the work of resistance 
contributed by the friction forces W r f cos ip and R p ; the area 
AFGB represents the work of resistance offered by the counter¬ 
recoil system; and the area OABC represents the work of resist¬ 
ance of the hydraulic brake, Rn. 

It will be observed that the values of the counter-recoil force 
( R s ) and of the hydraulic brake force (Rh) vary in magnitude 
throughout the length of recoil. 

133 . Hydraulic brake force.—The value of (Rh) for each 
point of the recoil can be determined after the proper deductions 
have been made for all the other forces at corresponding points; 
or from equation (51) 

Rh = R r +lV r ( sin ip — f cos if/) —R s — R p , (53) 

where Rh varies for each point of recoil. 

134 . Counter-recoil force.—The function of the counter-recoil 
system is to return the gun to battery after recoil. The force 
necessary to accomplish this may be determined from the follow¬ 
ing equation: 

R Sl = lVr(f cos ip + s'm ip) +R P , (54) 

where the values have the same significance as in equation (50), 
and R Sl is the value for R s at the beginning of recoil. The value 
of the coefficient / is usually estimated to be 25 per cent in order 
to take care of all conditions of lubrication that may arise aboard 
ship. The value of the packing gland resistance can be approxi¬ 
mated from a study of the mount design, and may be considerable 
for major caliber mounts. 


Recoil and Recoil Brakes 


141 


Springs may be satisfactorily employed for returning the gun 
to battery in the case of minor caliber mounts, and until recently 
were used for the same purpose for major caliber mounts, where 
the maximum angle of elevation did not exceed 15 0 . On account, 
however, of the recent large increase in caliber of major caliber 
guns, together with the large increase in the length of recoil and 
the maximum angle of elevation of these guns, the use of springs 
for returning the major caliber guns to battery is not practicable, 
and compressed air is used on the iater mounts. 


CYLIDER SECURED TO SLIDE 



typical counter-recoil system MINOR CALIBRE mounts 


Fig. 19. 



Fk. 20 . —Typical Counter-Recoil System for Turret Mounts. 


Fig. 19 shows a typical application of springs to a minor caliber 
mount; Fig. 20 shows a spring installation as applied to turret 
mounts. The springs are assembled with sufficient initial com¬ 
pression to bring the gun to battery against the forces of gravity 
and friction as determined from equation (54) for the maximum 
angle of elevation. As the gun recoils, the springs are further 
compressed, and, as a result, the spring resistance R s constantly 
increases from the beginning to the end of recoil, so that the value 
of R s at the end of recoil is usually 100 per cent greater than its 

























































142 


Naval Ordnance 


value (R$i) at the beginning of recoil. The proper allowance 
may easily be made for the variation of the magnitude of the 
force R s for each point of the recoil. In Fig. 11, the ordinate AF 
represents the value R s , at the beginning of recoil, and the ordi¬ 
nate BG the value of R, at the end of recoil. Where springs are 
used, AB is a straight line, since the spring force varies directly 
as the amount of compression of the spring. 


DIFFERENTIAL PISTON 



Fig. 2 i . —Typical Pneumatic Counter-Recoil System Major-Caliber 

Mounts. 


DIFFERENTIAL PISTON 



Fig. 22. 


In the case of compressed air, the initial force R Sl is derived 
from the compression of the air. Figs. 21 and 22 represent a 
typical compressed air (pneumatic) counter-recoil system as 
applied to major caliber mounts. The air is compressed to from 
300 to 1600 pounds per square inch initial pressure, and this pres¬ 
sure is held practically indefinitely without leakage by the use of 
special packings. During recoil, the pressure is increased from 
40 to 50 per cent above the initial pressure. In the case of com¬ 
pressed air, line AB, Fig. 18, will not be a straight line. 
































































































Recoil and Recoil Brakes 


M 3 

Since the time interval of recoil is small, we may without great 
error assume that compression takes place without loss of heat, 
and that the compression is adiabatic; in which case the pressure 
at any point may be determined from the following equation: 

P '= P '{W ( 55 ) 

where P 1 is the initial pressure; V x is the initial volume; P 2 is 
the final pressure; V 2 is the final volume; and K is a constant 1.41. 

Having determined the value of the pressure for each point 
of the recoil, the value of R s and R 2 for each point may be 
determined. 

135. Forces acting on the gun during recoil. —It is important 
that the jump of the gun between the time the gun pointer 
“ wills to fire” and the time the projectile leaves the gun shall be 



R, 

Fig. 23. 


the least possible amount. The reasons for this are obvious. On 
this account, it is desirable and necessary that the forces acting on 
the gun, including those due to the powder gases and the forces 
resisting recoil, be so disposed that the gun will not be lifted from 
its bearing in the bottom of the slide until after the projectile 
leaves the gun, and that the only appreciable movement of the gun 
before this time will be in the direction of the axis. 

Before the gun is fired, the forces acting are the weight of the 
recoiling parts W r and the reactions R 1 and R 2 , Fig. 23. Under 
the action of these forces, the gun rests in the bottom of the slide 
which supports it. 

When the gun is fired and the powder gases begin to act, the 

\V 

forces of inertia —— £ a, hydraulic brake resistance R h , counter- 

«S 

recoil resistance R s , friction, etc., begin to exert their effect. It is 
















































144 


Naval Ordnance 


important that the initial position of the gun, immediately before 
firing, be disturbed as little as possible under the action of these 
forces until the projectile leaves the muzzle. Under no condition 
should the effect of these forces be to lift the gun from its bearing 
in the bottom of the slide before the projectile reaches the muzzle. 
Whether such a condition exists in any design may be determined 
by writing the equation of forces and solving for the reactions 
R x and R 2 of Fig. 24. If these reactions in any case prove to be 
negative, the condition may be regarded as unsatisfactory. 



Writing these equations, we have 


R,+R 2 = lV r , 

( 56 ) 

or 


R 1 = Wr — R 2 , 

( 56 - 1 ) 

and 


R.^lVr-R,. 

(56-2) 


Taking moments about the center of gravity of the recoiling 
weights, W r , we have 

R 1 L 3 = R h M + -\-fR 1 s 1 + fR 2 z 2 + R 2 L 2 — R s n—PL 1 . (56-3) 

Substituting in equation (56-3) for R 2 its value from equation 
(56-2), we get 

R 1 L 3 = R h m+ +fR 1 z l +fz 2 (Wr-R 1 ) + 

g L i {W r -R 1 )-R,n-PL 1 . (56-4) 

Simplifying, we have 

R*tn+ +fWrZ 2 + W r L 2 -R s n-PL i . 

Ri= - £ - 


T 3 f 3 i + f 3 2 T b. 


( 56 - 5 ) 





























































Recoil and Recoil Brakes 


145 


Substituting in equation (56-5) for R x its value from equation 
(56-1) and transposing, we have 



R 2 = lVr- 


( 56 - 6 ) 


L 3 — fz 1 +fz 2 +L 2 


To insure a steady mounting and to reduce the jump of the gun 
in the slide to a minimum, it is desirable to keep the distance [ d , 
Fig. 24] of the center of gravity of the recoiling weights below 
the axis of the gun as small as possible. On the later design of 
mounts, the center of gravity of recoiling parts is located approxi¬ 
mately on the axis of the gun. For the same reason, the mount 
should be designed so that the counter-recoil cylinders are located 
on the side of the gun opposite to the hydraulic brake cylinder 
(recoil cylinder). 

136 . Pneumatic counter-recoil system.—A pneumatic counter¬ 
recoil cylinder as applied to major caliber mounts is illustrated 
in Fig. 21. Three such cylinders are mounted on each side. The 
cylinders are secured to the gun slide in much the same way as 
has been the practice heretofore in the case of spring cylinders. 
The piston rods are attached to a yoke that recoils with the gun. 
The piston rod, piston, and the liquid around the piston rod move 
together during recoil. The liquid and piston arrangement shown 
is for the purpose of lubricating the cupped leather packings and 
to facilitate the packing of the air at the high pressures use. The 
initial pressure of the air in the particular mount illustrated is 
1200 pounds per square inch. This pressure is increased to 2100 
pounds at the extreme recoil position. The counter-recoil valve 
shown in the figure opens during recoil and permits the air in the 
forward section of the cylinder to pass into the rear section of the 
cylinder, the valve closing at the end of recoil. A small orifice in 
the valve connects the forward and rear portions of the cylinder 
and the air flows from the rear portion of the cylinder to the 
forward portion until the pressures in the two portions of the 
cylinder are equalized. The function of this valve is to regulate 
the flow of air from the rear to the forward chamber during 
counter-recoil by throttling, so that the return of the gun to 
battery will not be too violent. The final movement of the gun to 
battery is checked in the usual manner by the counter-recoil 
plunger and dash pot which is part of the recoil system. 




146 


Naval Ordnance 


The success of the pneumatic counter-recoil system depends on 
the reliability of the packing. It has been found by actual experi¬ 
ence that if the packing is properly designed, air at high pressure 
can be retained for long periods with no diminution in pressure. 
Fig. 22 shows to_larger scale the feature of the packing which is 
a part of the system shown to smaller scale in Fig. 21. 

Two practical difficulties are experienced in packing air at 
high pressures. First, it is difficult to get castings of sufficient 
density and homogeneity to prevent the leakage of the air through 
the pores of the metal. The second difficulty is that of packing 
air under high pressures owing to the tendency of cupped pack¬ 
ing and other forms of packing to dry out and permit the air to 
escape. The first difficulty can be overcome to a great extent by 
the use of forged material instead of castings for all parts in¬ 
closing the air. The second difficulty is overcome by introducing 
a liquid chamber between the air chamber and the atmosphere, 
as shown in Fig. 22. By means of the differential piston shown, the 
liquid is under a higher unit pressure than the air, which it packs, 
so that the liquid tends to escape through the differential piston 
to the air chamber or through the piston rod packing to the 
atmosphere. Whereas great difficulty is experienced in packing air 
by the usual methods, no great difficulty is experienced in packing 
liquid at the same or increased pressures since the liquid keeps 
the packing moist and the surfaces with which it comes in contact 
well lubricated. Special care must be exercised, however, in the 
selection of the material for the cup packing, and also of the 
material for the liquid, in order that galvanic action will not be set 
up between the ferrous and non-ferrous parts with which it comes 
in contact. 

The difference in unit pressure between the liquid and air is 
determined by the proportions of the differential piston. The 
area of the surface exposed to the air is greater than the area 
of the surface exposed to the liquid by an amount equivalent to 
the area of the piston rod. 

During recoil, the liquid in the liquid chamber lubricates the 
surfaces of the cylinder and piston rod so that it is necessary to 
replenish the liquid in this chamber from time to time as the 
mount is used. The piston rod of the differential system which is 


Recoil and Recoil Brakes 


147 


exposed to the atmosphere serves as an indicator from which can 
be determined the time when it is necessary to replenish the liquid. 

137 . Stresses in deck structure due to firing.—The bolts 
securing the mount to the deck and the deck structure itself must 
be capable of withstanding the weight of the gun and mount and 
the turning moment produced by the reaction of the slide trun¬ 
nions in the trunnion seats of the carriage. 

The forces acting on the deck structure when the mount is fired 
are shown in Fig. 25. 



These forces, R lt R 2 , and H s may be determined as follows: 
For equilibrium, the summation of all horizontal forces is 
equal to zero, or 

Rr H 8 — 0. ( 57 ) 

Taking moments about R, we get 

R,h —IVm — RJ =o, (57-i) 

or 

(57-2) 


Taking moments about R 2 , we get 

Rrh + W (l — m ) —R x l= o, 
or 

D _ Rrh + W(l-m) 
K t - j . 


(57-3) 

(57-4) 


Equations (57-2) and (57-4) give the value of the reactions 
at the beginning of recoil. The value of the reactions with the 



























148 


Naval Ordnance 


gun at extreme recoil may be determined by making the proper 
allowance for the movement of the weight of the recoiling parts 
through the distance of recoil. 

138. Standard trunnion pressure formula. —In order to have 
a uniform, simple formula available for comparing the stresses 
set up by various guns and mountings when extemporizing new 
armament for vessels, or in the preliminary stages of the mount 
design where it is necessary to form some idea of the forces acting 
in advance of the completion of the design, the Bureau of Ord¬ 
nance has adopted certain formulas for computing the constant 
resistance force R r and the resultant trunnion pressure due to this 
force and the weight of the oscillating weights. 

It has been found that sufficiently accurate results for the 
purposes above mentioned can be obtained if we assume the 
velocity of free recoil curve, function of time (Curve No. 1, 
Fig. 9), is a parabola. With this assumption, it is possible to 
derive a comparatively simple equation for the constant retarding 
force, and the time of retarded recoil t 4 . 

Proceeding on the basis of the above assumption, we may write 
for the velocity of free recoil at any time 


V f =V2pt, 

where 2p is the latus-rectum of the parabola and Vf and t have 
the same significance as in the previous discussion. 

As previously shown, the value of R r may be expressed as 
follows: 


Rr = 


WrVf 3 

gh * 


( 35 ) 


where R r is the constant resistance necessary to check the recoil 
in the distance N r4 , Vf z is the maximum velocity of free recoil, 
and t 4 is the time of retarded recoil. 

Vf 3 may be obtained from the equation 


T 7 _ (PV p + 47 OOW) 
f3 ~ W r 


( 21 ) 


Assuming the velocity of free recoil, function of time, to be a 
parabola, and referring to Fig. 9, the area under Curve No. 1 




Recoil and Recoil Brakes 


149 


from the origin to the point of maximum velocity of free recoil 
( Vf 3 ) will be 

Wnh* 

Remembering that the area under the curve of velocity of 
retarded recoil is the length of recoil S ri , we may write (see 

Fig- 9 ) 

Sr t = V h (U-‘z)+Wnt a -. 

From which 


4 ~ v~. 

V f 3 


( 58 ) 


By substituting the value of t 4 equation (58) in equation (35), 
we may obtain the value of the constant resistance R r . It is cus¬ 
tomary to increase the value of R r obtained from equation (35) 
by 10 per cent to 25 per cent to cover irregularities that may be 
expected due to the semi-empirical nature of the equation. 



The trunnion pressure Rt is the resultant of the constant resist¬ 
ing force R r and the weight W 1 of the oscillating parts supported 
by the trunnions. 

These two forces may be represented in magnitude and direc¬ 
tion by the lines shown in Fig. 25a. 


*The area under the curve at any point is 

area = f V f dt. 

J to 

Substituting for Vt its value V2 pt and integrating between the limits 
/ 0 = o and t = t 3 , we have 

area=\ / ^y' o ' 3 M-V^X 3[/*] o \ 

Substituting for 2 p the value obtained by subst-'tuting Vn for V f and / 3 
for t in equation Vr— \/ 2 pt, and simplifying, 

area=^X§B f I 0 r3 = IF,3f.,. 

V's 0 








Naval Ordnance 


150 


Where if/ is the maximum angle of elevation and Ft the trunnion 
pressure corresponding to this angle. 

Solving the triangle of forces, we have 


Pt = W x sin ( 9 °° ~h ^ ) 
2240 sm A 


(59) 


where P\ is in tons (2240 pounds) and A the angle obtained from 
the relation 

tan $(B — A) _ (. R r —W x ) / 6o \ 

tan^(90 — B) (R, + IV 1 ) ' 

Equations (58), (35), and (59) are regarded by the Bureau 
of Ordnance as standard formulas for computing trunnion pres¬ 
sures in all preliminary calculations. They are not sufficiently 
accurate, however, for computing throttling orifices, these being 
computed by the methods previously discussed. 


RECOIL CYLINDER 
PRESSURE 
IN l8S. PER SQ in. 
3000 : 



139. Test of recoil system at the proving ground.—When a 

new type of mount is proved at the Naval Proving Ground, it is 
the practice to take indicator cards showing the pressures in the 
recoil cylinders and the counter-recoil dash pots together with 
velocity of recoil cards. 

140. Recoil cylinder pressure indicator cards. —An indicator 

similar to a steam engine indicator is attached to the recoil cylin¬ 
der and the drum to which the indicator card is attached is con¬ 
nected by a cord to the gun yoke. The pressure occurring in the 
recoil cylinder during recoil is recorded on the indicator card, so 
that the pressure for each point of the recoil is shown. Fig. 26 
shows a typical indicator card for a 16-inch mount. 

















Recoil and Recoil Brakes 


151 

141. Velocity of recoil curves.—The velocity of recoil is 
measured by means of an instrument known as the Siebert veloci- 
meter, named after its inventor. A steel tape is attached to a part 
of the gun. The tape moves past a pointer attached to a tuning 
fork as the pointer vibrates in a direction transverse to the direc¬ 
tion of movement of the tape. During recoil a line is traced by 
the pointer on the tape. The record made consists of a number 
of waves of varying lengths; the length depending on the speed 
of the tape. The rate of vibration of the tuning fork being known, 
the time of travel may be found by measuring the length of the 
waves and dividing by the known period of the tuning fork. In 
this manner, the velocity of recoil at all points may be determined 
and the velocity of recoil curve constructed from the data obtained. 








CHAPTER V. 

NAVAL RIFLED GUNS. 

General Discussion—Definitions. 

142. A gun is a mechanical device, consisting of a tube closed 
at one end at the moment of firing, capable of containing a pro¬ 
jectile and a propelling charge, and of so controlling the explosion 
of the charge as to discharge the projectile with a high velocity. 

143. A mortar is a short, heavy gun using a high angle of fire. 

144. A rifle is a gun whose bore has cut on its surface a number 
of spiral grooves, into which the soft metal of the rotating band 
on the projectile is forced, thus- imparting to the projectile a 
motion of rotation. The raised portions between the grooves are 
called lands. (See Plate I.) 

145. A cast gun is one made by casting metal in a mold in the 
form of a gun, or approximately the form. Iron, bronze, and 
steel have been thus used. Cast guns are used in several foreign 
navies, but are used in our navy for drill guns only. 

146. A built-up gun is any gun made up of dififerent parts, the 
idea being to get an assemblage of parts best able to resist tbe 
pressures of the powder gas. The gun may be built up of dififerent 
metals. The most usual forms are: (i) The built-up gun with 
initial pressure obtained by shrinkage, the exterior parts being 
heated to go over the interior parts; and ( 2 ) the “ wire-wound ” 
gun. 

147. A low-power gun is any gun having a low muzzle velocity 
and a low pressure. 

148. A high-power gun is any gun having a high muzzle 
velocity and a high pressure. 

As the terms “ low-power ” and “ high-power ” are relative, no 
fixed velocity and pressure can be stated to distinguish between 
the two 

149. The bore of a gun is that part of the interior of the tube 
that is of uniform diameter from the “ powder chamber ” (origin 
of rifling) to the muzzle. 


i53 


154 


Naval Ordnance 


150. The chamber of a gun is the space allotted to the powder 
charge, and is that part of the interior of the tube between the; 
“ bore ” and the face of the breech plug when closed. The 
“ chamber ” is made larger in diameter than the “ bore ” in order 
to reduce its length, and so give a greater length of travel for the 
projectile in the “ bore.” The ratio of the diameter of the 
“chamber” to the diameter of the “bore” is called chambrage. 

151. The caliber of a gun is the diameter of a cylinder which 
touches the highest points of all the lands. 

The word caliber is also used in connection with the length of 
the gun, meaning the length of the gun divided by the diameter 
of the bore. That is, it is the over all length of the gun from the 
breech face to the muzzle face expressed in the caliber of the gun 
as units. Thus a 50 -caliber 12 -inch B. L. R. is 50 calibers, that is 
50 feet, in over all length, from the breech face to the muzzle face. 
A 11 allowance is sometimes added for the breech-plug housing. 

152. The gun metal thickest over the chamber.—This is the 
case because at the point over the seat of the powder charge the 
pressure of the powder gas is the greatest. The powder pressures 
gradually decreasing toward the muzzle, the strain on the gun 
becomes less, and hence the gun may taper forward. 

153. Parts of a gun.—A gun as viewed from the outside has 
the following parts: Breech, rear cylinder, slide cylinder, chase, 
muzzle. (See Plate I.) 

The breech is the rear end of the gun, while the muzzle is the 
front end, whence the projectile issues. 

The rear cylinder, at the breech end of the gun, is that part 
over the chamber where the metal is thickest. 

The slide cylinder is that part of a gun forward of the rear 
cylinder which fits in the slide and moves through it in recoil. 
It is fitted with a key that is contained in a keyway in the slide 
which prevents the gun from turning in the slide, restricting it to 
longitudinal motion only. This part of the gun is made truly 
cylindrical to fit snugly in the slide. 

The chase is the sloping portion forward of the slide cylinder 
extending to the muzzle, whether in one taper or in stepped tapers 
caused by hoops. 

I he end of the chase forms a curve at the muzzle of increased 
diameter, forming what is known as the “ bell muzzle.” The metal 


Naval Rifled Guns 


155 


is increased at that point to give greater strength, to prevent 
enlargement of the bore due to high muzzle pressures. 

The trunnions are two horizontal cylindrical projections at 
right angle to the axis of the bore of the gun, the purpose of 
which is to support the gun on the carriage. They are located at 
or near the center of gravity of the gun, and form the axis around 
which it moves in elevation. In the United States Navy it is 
customary to have the trunnions slightly towards the breech, thus 
making the gun “ muzzle heavy ” when empty, but balanced when 
loaded. 

In cast guns the trunnions are in one with the gun. Built-up 
guns are made trunnionless , the gun being supported by the 
“ slide ” or “ sleeve ” within and through which the gun moves 
in recoil, the trunnions in this case being cast with the slide. 

The trunnions rest in “ seats ” on the gun carriage. 

The recoil is checked by hydraulic or pneumatic cylinders 
attached to or cast with the slide, the pistons of which are con¬ 
nected by their rods to a “yoke ” around the rear cylinder of the 
gun. Sometimes this arrangement is reversed, the cylinders being 
attached to the gun and the pistons being held fixed. The slide 
is usually bushed with bronze or gun metal to prevent the steel 
of the gun from sliding on the steel of the slide. Heavy grease is 
used as a lubricant between the surfaces of the gun and slide. 

154. Breech-loading rifles and rapid-fire guns were terms 
previously used to designate different types of guns. However, 
all modern naval guns are breech-loading, all are rifled, and all 
are more or less rapid-firing; hence the terms have been aban¬ 
doned. Instead, thereof, the terms bag guns and case guns have 
been adopted. 

155. Bag guns are guns that do not use metallic cases for the 
powder. A mushroom and gas-check pad are therefore required 
to prevent the powder gases, under the high pressures of ex¬ 
plosion, from escaping to the rear around the plug. 

156. Case guns are those in which a metallic powder case is 
used, this case preventing escape of gas to the rear, so that no 
mush-room and gas-check pad are required. 

157. Field guns are of 3 -inch caliber and are supplied with 
field carriages for use on shore. 


Naval Ordnance 


156 

158. Boat guns are supplied with mounts for use in small boats. 

159. Automatic guns are those in which the force of explosion 
is used to eject the fired cartridge-case and load another cartridge. 
When ammunition is properly supplied, no force but pressure on 
the trigger is required for continuous fire. 

160. Semi-automatic guns are those in which the force of 
explosion ejects the fired cartridge-case and leaves the breech so 
that it closes automatically when another cartridge is properly 
inserted. 

161. Machine guns are automatic rifles, using small-arms 
ammunition. 

162. Small arms include rifles that are fired from the shoulder, 
and pistols that are fired from the hand. 

163. Sub-caliber guns.—A gun is called a sub-caliber gun 
when it is used mounted inside or outside a larger gun, for short- 
range gunnery practice. One-pounders and small-arms rifles are 
used for this purpose. 

164. Designation of guns.—Guns are usually named or desig¬ 
nated either by (1) caliber in inches, followed by the length of 
bore in calibers and the mark of the gun; or by (2) weight of 
projectile expressed in pounds for small-caliber guns (1-pounders 
to 6-pounders), followed by the mark of the guns. Thus: 14- 
inch, 45-caliber, Mark I, Mod. I. 

All guns of the same caliber, but of a different design, are 
distinguished from one another by being given different marks. 
The first design built of a caliber is called Mark I. If a new 
design is built with either new exterior or new interior dimen¬ 
sions, giving different ballistics from the previous design, this 
design is given a new mark, as, for instance, Mark II. If, how¬ 
ever, a finished gun is modified, it retains the same mark, fol¬ 
lowed by a modification number, as 12-inch, Mark VII, Mod. II 
(the second modification made on Mark VII, 12-inch gun). Thus 
the 14-inch, Mark I gun, on being relined, would be designated as 
14-inch, Mark I, Mod. I gun. 

The usual service method is to write the caliber and the mark 
only ; thus : 8-inch, Mark V, Mod. I. 

This system of marking is carried out throughout ordnance, not 
only for guns, but for gun mounts, breech mechanisms, sights, 
powder tanks, firing locks, and, in fact, most articles that are 
units in themselves. 


CHAPTER V, PLATE t. 


-CHAMBER 


C HAMBER FROHT SLOP E- ^ r-SHEU-CEKTERINR SLOPE 

’’’ -» J*" BAND REAR SLOPE 

i 


— band cylinder. 

1 BAH D FRONTSLOPE 


— BANDSEAT 


► origin of Rifling. 



DRIVING___ 

/////////////, 

hook Ri fling - 





— BREECH HOUSING: 



1 






b 

H. 




^-LOCKING RING B, 

TUBE. A7 



CHAMBER 


CHAM3CR FRONT sc 

p 

j —sheh 

CENTERING SLOPE 




1 

1 

— BAND SLOPE 











— 

-ORIGIN OF RIFLING. 


GUNS MISCE.LLAvNE.OUS. 


GUN NOMENCLATURE. 


f-T3Vj-m.-zniN 






















































































































































































































































































































Naval Rifled Guns 


157 


165 . Guns are classed on board ship (1) by calibers, and (2) 
by batteries. 

(1 ) Classed by calibers, they are called “ major,” “ inter¬ 
mediate ” and “ minor ” caliber guns. 

Major caliber guns include all guns of 8-inch and above. 

Intermediate caliber guns include all 4-inch, 5-inch, 6-inch and 
7-inch guns. 

Minor caliber guns include all calibers greater than “ small 
arms ” and less than 4-inch. 

(2) Classed by batteries, the guns of a ship consist of " main,” 
“ secondary ” and “ anti-aircraft ” batteries. 

The main battery in turret vessels includes all turret guns. In 
all other vessels it includes all guns except those specially designed 
for use against aircraft or for use in throwing depth charges. 

The secondary battery in turret vessels includes all guns except 
turret guns, anti-aircraft guns, and depth charge projectors. 

The anti-aircraft battery includes all guns carried for primary 
use against aircraft. 

The term “ depth charge projector” includes any apparatus for 
launching depth charges. 

Rifling of Guns. 

166 . Advantages of rifling. —The penetration of oblong pro¬ 
jectiles, other things being equal, is much greater than can be 
realized with spherical shot, while the bursting charge of oblong 
shells is as great as, or even greater than, that of spherical shells, 
on account of their greater length. These are very substantial 
advantages; but to secure them it is essential that the oblong pro¬ 
jectile should keep point foremost in its flight; otherwise it would 
have neither range, accuracy nor penetration, but would waste its 
energy beating the air. 

The only way to secure steadiness of flight to an oblong pro¬ 
jectile is to keep its geometrical axis in the tangent to the tra¬ 
jectory it describes by giving it a high rotary velocity about its 
axis, thus imparting to it the properties of a gyroscope, whereby 
it resists angular motion. This is accomplished by rifling, as it is 
called ; that is, by cutting spiral grooves in the surface of the bore 
into which a projecting copper band, securely encircling the pro¬ 
jectile near its base, is forced as soon as the motion of translation 


158 


Naval Ordnance 


begins, thus giving to the projectile a rotary motion in addition to 
its translation as it moves down the bore. The rifling may be such 
that the grooves (or rifles ) have a constant pitch—that is, make a 
constant angle with the axis of the bore—or this angle may 
increase gradually. In the first case the gun is said to be rifled 
with a constant twist, and in the second ca*se with an increasing 
twist. In all cases the twist at any point of the bore is measured 
by the linear distance the projectile would advance while making 
one revolution, supposing the twist at that point to remain con¬ 
stant. This linear distance is always expressed in calibers, and is 
therefore independent of the unit of length employed. (See Art. 
628.) 

< Gun Construction. 

167 . Present requirements for guns demand muzzle velocities 
of from 2500 to 3150 feet per second. Lower velocities give less 
striking force, and, more important still, a projectile fired at low 
velocity would describe a curve so high in the air, for long ranges, 
that hits could not be made unless the range were known with 
great accuracy. Since the accurate determination of range is the 
most difficult problem in naval gunnery, the high-power gun is a 
necessity. High velocity of projectile is produced, of course, by 
high pressure upon it while traveling through the bore. No heavy 
gun of a single piece of metal, whether cast or forged, could with¬ 
stand the high pressures generated within the gun, and therefore 
the peculiar methods of modern gun construction are employed. 

A gun may be considered as a tube designed to withstand a 
given pressure from within, throwing a projectile which shall pro¬ 
duce certain effects at given distances. In constructing such a 
tube, we must first consider what pressures it will have to with¬ 
stand at the various points of its length, and then make it strong 
enough to insure perfect safety. The bore should also be of such 
material as to stand the wear and tear of firing a large number of 
rounds without being so damaged by expansion or abrasion as to 
interfere with the shooting. 

Not only must be gun be sufficiently strong, but it must not 
be too heavy ; so it is important that the material shall be arranged 
in such a manner that there may be no waste of its strength—in 
fact, so arranged that every part shall perform its own share in 
withstanding the pressure from within. Shortly after the shot 


Naval Rifled Guns 


159 


begins to move, the pressure inside the gun decreases, and con¬ 
tinues to decrease as the projectile approaches the muzzle; for 
this reason the gun is made stronger at the powder chamber than 
toward the muzzle end. 

The designing of guns, like the manufacture of other ordnance 
material, is the gradual development and improvement of a type, 
as the result of years of practical experience in perfecting models 
as needed to meet the increasing ballistic demands. 

168. The three general subdivisions of the preliminary gun 
design are: (1) The mechanical, (2) the ballistic, and (3) the 
service conditions. 

( 1 ) The mechanical conditions. —It is necessary that the gun 
should be able to resist the pressures developed in the bore when 
fired. This is accomplished by the choice of a suitable material, 
and by a careful determination of the method of assembling the 
various constituent parts of the gun. 

(2) The ballistic conditions. —The gun is designed to produce 
a certain ballistic result under the best possible conditions. The 
formulas of interior ballistics enable one to determine the weight 
of charge, the density of loading, and the quickness of the powder 
to be used. From these are deduced the dimensions of the powder 
chamber. 

(3) The service conditions. —The gun should meet the require¬ 
ments of service afloat in regard to loading, elevating, the oper¬ 
ation of the breech mechanism, relining of gun, etc. These 
requirements affect the forcing cone, the outline of the powder 
chamber, the type of breech mechanism, the center of gravity, 
and the weight. 

169. Stresses. —Looking simply to the construction of a gun 
cylinder, we find that the two principal stresses to which such a 
cylinder is subjected upon the explosion of a charge are, first, a 
circumferential or tangential stress or tension, coupled with a 
radial stress, tending to split the gun open longitudinally; second, 
a longitudinal stress tending to pull the gun apart in the direction 
of its length. 

It has been ascertained as the result of experiment that the 
greatest stress experienced by the metal of the gun is the tensile 
stress set up in the direction of its circumference by the pressure 
of the powder gases; in addition, it also experiences a longitudinal 
stress. 


i6o 


Naval Ordnance 


The least complicated method of making a gun would seem to 
be that of casting it as a homogeneous hollow cylinder; but if we 
take such a tube, made of one material throughout, we find that 
its tangential strength to resist a pressure from within does not 
increase uniformly with its thickness. 

If now we exert pressure upon the tube from without, the 
initial pressure exerted by the powder gases must first neutralize 
this outside pressure before it can subject the tube to any addi¬ 
tional tensile stress. The amount of the external pressure must 
not, however, exceed the elastic limit of the metal, as otherwise 
permanent deformations would be produced in the inside layers 
of the gun. The amount of the external pressure must be so com¬ 
puted that the tensile strength of the metal of the bore of the tube 
will be fully utilized in firing, and it must therefore merely equal 
the difference between the gas pressure and the limit of resistance 
to tensile strain of the metal. 

We find, practically, that with a given material we soon reach 
a limit beyond which any additional thickness of wall aids but little 
in enabling the cylinder to withstand pressure. Supposing the 
metal to be incompressible, this limit is taken at about half a 
caliber, so that—for example in the cylinder of an hydraulic press 
—if the thickness of the walls be equal to one-half the diameter of 
the piston which works inside, then the cylinder will be nearly as 
strong as if it were ten times as thick. 

It is generally conceded that no possible thickness can enable a 
simple cylinder to bear a continued pressure per square inch from 
within as great as the tenacity of a square-inch bar of the same 
material; that is to say, if the tensile strength of cast iron be 12 
tons per square inch, no cast-iron gun, however thick, could bear 
a charge which would exert that pressure on each square inch, 
for, on the first round the interior layer would be ruptured before 
the outer portion could come into play, and every succeeding round 
would tend to make matters worse. 

From the above it is clear that guns made by simply casting or 
forging iron, bronze, or steel into homogeneous cylinders cannot 
be made strong enough. The working pressure which we require 
a high-power gun to withstand is not less than 18 tons per square 
inch, and we require, further, that this pressure shall not strain 
the gun beyond the elastic limit of the metal, in order that the bore 


Naval Rifled Guns 


161 


of the gun shall not be permanently enlarged. The elastic limit of 
cast steel is from 15 to 20 tons per square inch, and since steel 
has a higher elastic limit than either iron or bronze, allowing 
a margin of safety, it will not do to make a high-power gun 
of cast homogeneous metal even when we use steel. We must 
resort, then, to what is termed the built-up system, and it can be 
shown mathematically that a built-up gun, properly constructed, 
of the same dimensions and material as a homogeneous gun, is 
• much stronger than the latter. 

170 . Having decided upon the built-up gun, we accept as 
axiomatic and fundamental the following: 

Basic law of gun construction.— No fiber of any cylinder in 
the gun must be strained beyond the elastic limit of the metal 
of that cylinder. 

Attention is called to the word “ strained ” in this law. This 
law is stated again in paragraph 188 in a much fuller form, and 
we see that it is not the forces or “ stresses ” acting (for one may 
balance another), but the “ strain ” or deformation resulting from 
their joint action that limits us. 

171 . To satisfy this law there are two “principles” of con¬ 
struction : (1) “ varying elasticities ” and (2) “ initial tensions.” 

(1) The principle of varying elasticities.—This consists of 
placing that metal which stretches most within its elastic limit 
around the surface of the bore, so that by its enlargement the 
explosive stress is transmitted to the other parts exterior to it. 
This method is exemplified in guns which have a steel tube sur¬ 
rounded by wrought-iron coils, and in the Palliser system, in 
which a wrought-iron or steel tube is surrounded by cast jron. 
With different grades of steel—high and low steel, for example— 
the steel which shows the greater elongation within the elastic limit 
is the more suitable to be placed next to the bore. Carrying out 
this theory in practice is another matter, because in the case of 
very long tubes there is more difficulty and uncertainty of manu¬ 
facture with the higher grades of steel than with the lower, and 
the difficulty increases with the size. For this reason the principle 
of varying elasticities is only applicable where the different parts 
of a gun are made of different metals. 

(2) The principle of initial tensions.—This consists in giving 
to the exterior portions of the gun a certain initial tension, gradu- 


12 


Naval Ordnance 


162 

ally decreasing toward the interior, and giving to the interior parts 
a certain normal state of compression by the grip of the outer 
cylinders and coils. 

If by the system of initial tensions the interior can be put in 
a state of compression, within the elastic limit of the metal, the 
amount of that compression is so much additional strength, since 
it must first be overcome before the powder gases can exert a 
tension on the fibers of the interior tube. In order to exert com¬ 
pression, then, the outer coils or hoops must be in a state of 
normal tension, and in addition to that they must have a margin 
of strength within their elastic limits to withstand the additional 
tension transmitted by the explosion of the charge, this additional 
tension being, of course, much less than would be put upon free 
metal next the bore. 

The exact amount of tension and compression for all parts of 
the gun when at rest, or when resisting the explosion of the 
charge, so that all parts shall be strained to a point not exceeding 
their elastic limit, is a matter for mathematical calculation, and 
is treated at length in works on the theory of gun construction. 

Owing to the difficulty of obtaining the proper graduations of 
elasticity from cylinder to cylinder, as is necessary under the 
“ principle of varying elasticities,” we have adopted the “ principle 
of initial tensions ” for the construction of the guns for our 
service. 

Having adopted “ initial tensions ” as the principle of construc¬ 
tion to follow for our guns, it remains to describe, in general 
terms, how the thickness of the walls and the “ shrinkages ” are 
determined. 

172. Thickness of walls.—By the principles and formulas of 
Interior Ballistics, Chapter III, we can find the pressure of the 
powder gases at any point of travel of the projectile through the 
bore. By solving for a number of points and plotting them on 
the axis of the gun, with the pressures as ordinates and the travel 
of the projectile as abscissae a curve of pressures can be con¬ 
structed for a given powder that will approximate to the truth for 
practical purposes ; a good margin of safety is always allowed, and 
the various thicknesses of metal to withstand the pressures at 
different points of the length of the bore follow at once, the caliber 
and length of the gun having previously been fixed by the amount 
of work the gun is expected to perform. 


Naval Rifled Guns 


163 

173 . After the preliminary drawing of the gun has been com¬ 
pleted, the elastic strength to resist powder pressure is computed 
at all points, together with the shrinkages. The strength curve is 
then compared with the pressure curve, and if there is not a 
sufficient margin of safety, a readjustment of the dimensions of 
the parts of the gun is made, and the elastic strength is recom¬ 
puted. It is also necessary to compute the stresses which the parts 
undergo in the state of rest to determine that the tube will not be 
crushed by the shrinkage. 

An example of a pressure curve plotted with a strength of gun 
curve is shown in Chapter III, Plates II and III. 

174 . Shrinkage.—Practically, the compression of the interior 
and tension of the exterior are effected in manufacture, after the 
amounts for each have been calculated, (1) by shrinkage, (2) by 
forcing upon one another by hydraulic pressure two cylinders 
having slightly coned surfaces, or (3) by winding steel wire, or 
riband, over a steel tube. 

If the method of shrinkage be employed, the hoops or tubes to 
be shrunk on must be accurately bored, and the outer cylinder must 
be expanded by heat until it is sufficiently large to slip over the 
inner. The inner diameter of the outside cylinder when cold 
must be a little smaller than the outside diameter of the inner 
tube, and this difference of diameters is called the shrinkage. 
While the outer cylinder is cooling and contracting it compresses 
the inner one, making the diameter of the latter a little smaller 
than before. The amount by which the exterior diameter is 
decreased is called the compression. 

Again, the outer cylinder itself is stretched on account of the 
resistance of the inner one, and its interior diameter is slightly 
increased. This increase is called the extension. 

The shrinkage is always equal to the compression plus the 
extension, and the exact amount must be previously calculated by 
the known extension and compression of various metals under 
certain stresses and given circumstances. 

The principle of initial tensions, carried to an extreme limit, 
would be exemplified in the case of a gun composed of an infinite 
number of infinitely thin hoops properly shrunk together. When 
so assembled, the tension in a gun, when the powder pressure acts, 
would be uniform throughout the thickness. The greater the 


164 


Naval Ordnance 


number of hoops the nearer this theory is approached in practice, 
but there are practical difficulties in manufacturing, such as the 
accurate machine work necessary and the greatly increased cost; 
for this reason it is not considered practicable to use more than 
four layers in the case of guns now designed. In the case of wire 
guns, or ribbon-wound guns, this theory is better exemplified, and 
when successful manufacture is possible in these cases, stronger 
guns of the same weight must be the result. 

175 . The wire-wound gun.—As stated above, this is an ex¬ 
ample of the initial-tension system. The wire is wound in layers 
around an inner tube of steel. Each layer is wound with a differ¬ 
ent tension of the wire, and each exerts a compression on the 
layers which are inside of it. The result is that, when completed, 
the outer layers are in extension, gradually diminishing to the 
inner layers, which are in compression—all within the elastic limit. 
As wire can be made of enormous strength (as much as 200,000 
pounds per square inch tensile strength), this type of gun is the 
strongest for the same weight of any yet developed. 






CHAPTER VI. 

ELASTIC STRENGTH OF GUNS. 

Section I.—Preface. 

176. This chapter was first published as a small book, prepared 
primarily for use by the midshipmen at the U. S. Naval Academy, 
by Professor Philip R. Alger. 

It is here included in this general treatise on Ordnance almost 
verbatim, there being no changes introduced, but some of the 
deductions and derivations have been expanded to show more 
clearly how certain results are obtained. 

The chapter essays to present the subject of the elastic strength 
of guns as concisely as is consistent with clearness, and to that 
end treats only of steel guns of modern construction. 

The hypothesis that permanent set will not occur unless the 
resultant strain in some direction exceeds the limit of elastic strain, 
regardless of what the stresses may be, is adopted. This hypoth¬ 
esis appears to the writer to be the only reasonable one, but it 
is to be regretted that its truth has never been demonstrated 
experimentally. 

The longitudinal stress is taken to be zero, an assumption made 
by Claverino in his first treatise on the “ Resistance of PIollow 
Cylinders,” published in the “ Giornale d’Artiglieria ” in 1876, and 
adopted by Birnie in his exhaustive studies of the resistance and 
shrinkages of built-up cannon. 

Wire-wound guns, though built on the principle of initial ten¬ 
sion, are not treated here. The theory and formulas on this 
subject can be found in the original text on elastic strength by 
Professor Alger. 

A number of illustrative examples are solved in the text, and 
others, with their answers, follow each section. 

INTRODUCTORY. 

177. Stress and strain. —We give the name stress to a mutual 
action between the parts of a body, or between one body and 
another, causing or tending to cause them to move relative to one 

165 


Naval Ordnance 


i 66 


another; it is any pair of equal and opposite actions each of which 
is what is called a force. 

Thus, if a rope be stretched vertically downwards from A to B, 
we speak of the tension T of the rope as the force T acting down¬ 
ward on A, or as the force T acting upward on B, according as we 
are considering A or B; but we speak of the action in the rope, 
which tends to break it, as the stress in the rope. 

178 . We call the change of volume or figure of any solid or 
liquid under the action of force a strain. 

Thus, if a bar is lengthened or shortened, it is strained; a com¬ 
pressed liquid is strained; a stone, a piece of metal, or other part 
of any structure, is said to experience a strain if it be bent, or 
twisted, or compressed, or dilated, or in any manner distorted. 
Furthermore, any change in the configuration of a group of bodies 
whose relative positions are subject to fixed conditions is called a 
strain. Thus, any structure is said to strain when its different 
parts experience relative motion, as, for example, a ship “ strains ” 
in a seaway. 

179 . If we imagine any plane area within a strained body as 
forming a division between the parts of the body on either side 
of it, then the force which each of the two parts exerts upon the 
other is one of the pair of forces which constitute the stress on 
the area. In other words, the stress on any sectional area is the 
pair of equal and opposite actions which hold the area in its state 
of strain. 

180 . The intensity of stress is the number of units of force per 
unit of area. We shall always express it in tons weight, or pounds 
weight, per square inch ; and, for brevity, we shall use the word 
stress as meaning “ intensity of stress,” always applying the term 
“ total stress ” to the whole force acting on any area. If the inten¬ 
sity of the stress (/>) is the same at all points of a given area (A), 
the stress on the area is said to be uniformly distributed, and P 


p 

being the total stress on the area, we have p— . If the stress 

is not uniformly distributed, its intensity at any point is given 
d P 

by p — , where dP is the total stress on the elementary area dA. 


181 . Hook’s law.—Every stress is accompanied by a strain, 
and experiments show that in all solid bodies the strain is propor- 


Elastic Strength of Guns 


167 


tional to the stress which causes it, provided the stress does not 
exceed certain limits which vary with the material. This is what 
is known as Hook's lam—“ nt tensio sic vis ” (as the extension so 
the force). 

182 . The simplest form of stress is that which exists in a bar of 
uniform section to which equal and opposite forces are applied 
axially, tending to lengthen or shorten it. If the forces act to 
lengthen the bar, the stress is called tension, and if they act to 
shorten it, the stress is called compression; but mathematically 
considered compression is merely negative tension. 

The strains accompanying tension are an elongation in the direc¬ 
tion of the pull and a contraction in all directions perpendicular 
to it; while the strains accompanying compression are the reverse, 
i. e., a shortening in the direction of the push and an expansion in 
all directions perpendicular to it. These strains are elastic, that 
is, they disappear with the removal of the forces which caused 
them, so long as the tension—or the compression, as the case may 
be—does not exceed a value which is called the elastic limit of the 
material. Within that limit the strains follow Hook’s law. 

183 . If P be the total pull (or push) on the bar, and A be the 
area of its right section, the total stress on any such section is P, 

.... . . p 

and, since it is uniformly distributed, its intensity is p= . The 

elastic limit * is the value of p beyond which the strain ceases to 
be wholly elastic; if this value is exceeded, the bar takes a per¬ 
manent set, i. e., when released it will be found to be longer (or 
shorter) than it was originally. With some materials, notably cast 
iron, the elastic limit under compression considerably exceeds that 
under tension, but in the case of steel the difference, if it exists, is 
not important. The elastic limit of the steel forgings used in 
modern gun construction is from 35,000 to 75,000 pounds per 
square inch. 

184 . The modulus of elasticity.—Within the elastic limit the 
ratio of stress to strain is, by Hook’s law, a constant, and the value 
of this constant for the case of simple tension or compression is 

* Some writers use the term elastic limit to denote the greatest elastic 
strain under simple tension or compression, instead of the greatest stress 
causing only elastic strains. We shall use the term elastic limit of strain to 
distinguish the former concept, and shall use elastic limit to denote the 
elastic limit of stress. 


Naval Ordnance 


i 68 


called the modulus of elasticity and is denoted by E. That is to 
say, if e is the change of length per unit length under the stress 

p = —7 , then E = . 

r A e 

Since e is the relative, not the total, strain, it is an abstract num¬ 
ber, being, in the case considered, the total change of length of the 
bar (due to its tension or compression) divided by its length when 
free. Consequently £ is a quantity of the same kind as p and its 
value depends upon the units in which p is expressed. 

When p is given in pounds per square inch, E has the vAue 
29,000,000 for steel; when p is expressed in tons per square inch, 
E has the value 13,000. 

Evidently E is the stress which would double the length of a bar 
under tension (if it continued to obey Hook’s law to that point), 
since when e=i, p — E. 

It must be understood that E is the value of the stress on a right 
section of the bar divided by the strain perpendicular to that sec¬ 
tion, or in the direction of the external forces causing the strain; 
the strains at right angles to the axis of the bar, though propor¬ 
tional to the principal strain, are less in value, their ratio to it, 
determined by experiment, being, in this work, taken to have the 
value 

185. Example. —As an example, suppose a round steel bar, 
2 inches in diameter and 20 inches long, to be under a tension of 

P 

60 tons; then the stress on a right section of the bar is p=—^~ 
where A=nr 2 . But d = 2" ,'.r= 1", hence A = -k from which 
p = — = — = 19.1 per square inch; the strain in the direction of the 

7r 7f 


axis of the bar is e— 

h 


*9 1 = .00147" ; and the strain at right 
13000 

angles to the axis is , : OOI 4 7 —.00049". The length of the bar is 

3 

increased by the tension 20 X .00147 = .0294 inches, making its 


* This quantity is known as “ Poisson’s ratio ” from the great French 
mathematician. Its value varies for different materials, and for steel has 
been taken by different authorities as J4, l /z and J4. The best modern 
experiments assign to it a value in the neighborhood of )/$. 




Elastic Strength of Guns 


169 


strained length 20.0294 inches; and its diameter is diminished 
2 X .00049= .00098, making its strained diameter 1.99902 inches. 

If the force of 60 tons were applied to compress the same bar, it 
would be shortened .0294 inches and its diameter would be in¬ 
creased .00098 inches. 

Under tension the volume of the bar is increased in the ratio 
1 to 1 000488; while under compression its volume is diminished 
in the same ratio. 

186 . If more than one pair of equal and opposite forces act 
upon a body, the stress upon any sectional area of the body is the 
resultant of the stresses which would be caused by the pairs of 
forces acting separately; and the strain at any point due to the 



simultaneous action of all the stresses is obtained by simply super¬ 
posing the strains due to the different stresses taken separately. 

Thus, taking a rectangular right prism with equal and opposite 
forces acting normally upon each pair of its opposite faces, let X, 
Y and Z be the forces acting per unit area of the respective faces: 
then the stress on each right section perpendicular to the X axis 
will be X, tbe stress on each right section perpendicular to the V 
axis will be Y, and the stress on each right section perpendicular 
to the Z axis will be Z. Also, at each point in the prism, the 
resulting strains in the directions of the axes will be: 


(a) 

(b) 

(c) 




*( 0 

































170 


Naval Ordnance 


In these expressions e x , c y and e z are the changes of length per 
unit length in the directions of the X, Y and Z axes, respectively, 
and are plus when they are lengthenings and minus when they are 
shortenings, provided the stresses X-, Y and Z are given plus signs 
when they are tensions and minus signs when they are compres¬ 
sions. 

187 . Evidently if either Y or Z be of opposite sign to X, the 

X . 

strain in the X direction may be greater than and similarly 


the strains in the Y or Z directions may be either greater or less 
Y 7 

than and ~ respectively, according as X, Y and Z are unlike 

or like forces. If, for example, X = I5 tons per square inch 
tension, and Y and Z are each 15 tons per square inch compres- 

1 


sion, we have e x = 


E 


15+—+—) = - - 2 5 __ = .001923, and the 
3 3 / i3°oo 


prism would lengthen .001923 inches per inch of its free length 
instead of only = .001154 inches per inch, as would be the case 
if the stress X alone acted. 

188 . In our investigations of the strength of guns we accept 
the following principle: 

The total strain in any direction due to all the stresses is the 
measure of the tendency to yield in that direction, so that the limit 
of clastic strength is reached, not when the stress in any direction 
equals the elastic limit of the material, hut when the strain in any 
directio)i equals the strain which would be caused by the direct 
action of a single stress equal to that elastic limit. 

If, for example, a steel forging lias an elastic limit of 58,000 
pounds per square inch, i. e., if 58,000 pounds per square inch is 
the greatest simple tensile stress which the steel will withstand 
without permanent lengthening, then for the safe use of such a 
forging it is necessary, and sufficient, that at no point within it 

shall the strain at any time exceed 58 o°o = ,— 5 ^ OOQ _ — 002 
. . . , . E 29000000 

inches per inch in any direction. ^ 

189 . At any point in a strained solid there are always three 
planes, at right angles to one another, upon each of which the 
stress is wholly normal. These three simple stresses (tensions or 




Elastic Strength of Guns 


171 

compressions) are called the principal stresses at the point, and 
their directions are called the principal axes of stress. 

In the case we are about to investigate—a hollow cylinder under 
internal and external fluid pressure—the principal axes of stress 
are evidently radial, circumferential, and longitudinal (parallel to 
the cylinder’s axis), and the principal stresses, which we denote by 
p, t and q, are illustrated in Fig. 28, where one of the elementary 



prisms of which we imagine the cylinder to be composed is shown 
in equilibrium under their joint action. 

The strains in the directions of the principal axes of stress are 
called the principal strains; they are simple longitudinal strains 
(lengthenings or shortenings), and their relations to the prin¬ 
cipal stresses are those given by equations (1). 

190 . Since the external pressures with which we are to deal are 
compressive forces, it will be convenient to call the radial stress 
(/>) plus when it acts to compress the material of the cylinder, 
















172 


Naval Ordnance 


though continuing to call the circumferential stress ( t ) and the 
longitudinal stress (g) plus when they produce tension.* With 
this convention, equations (i) become: 


(a) c t - -~ 

(b) <■,,= -A- 

I'+f+y] 

,-*— 

(c) e q — ■ £ 

r * , p ' 

L 3 3 - 

J 


in which Ct is the strain in the direction of the circumference, e v 
the strain in the direction of the radius, and e q the strain in the 
direction of the axis of the cylinder, in each case a plus value 
indicating extension and a minus value compression. 

In the theory of elasticity it is shown that if an ellipsoid be constructed 
with semi-axes representing the principal stresses at a point, the stress upon 
any plane at the point is represented in magnitude and direction by a radius 
vector of the ellipsoid, which is called the ellipsoid of stress. Evidently, 
then, one of the three principal stresses acting at each point in a strained 
solid is the greatest stress at the point. In a similar way it is shown that one 
of the three principal strains at a point is the greatest strain at the point. 

Examples. 

(1) A round steel rod i inch in diameter and 6 feet long is 
found to stretch .07 inches under a load of 10 tons. What is the 
intensity of the stress on its transverse section, and what is the 
value of the modulus of elasticity? 

12.73 tons P er sq. i n -; 13,096 tons. 

(2) What length of uniform steel rod, hanging vertically, will 
just carry its own length, if the maximum allowable stress is 8 
tons per square inch (steel weighs .283 lb. per cu. in.) ? 

5277 ft. 

(3) The ends of a steel I-beam whose flanges are 8 inches wide 
rest on stone supports. If each support takes half the total load of 
20 tons, what should the length of bearing surface be, the safe 
compression stress for stone being 300 lbs. per square in? 

9.3 in. 


* See footnote under Art. 219. 






Elastic Strength of Guns 


*73 


(4) A bar of steel 2 inches in diameter is bent so that its axis 
forms the arc of a circle of 372 ft. diameter. What is the greatest 
strain at any point of the transverse section, and what is the 
greatest stress? (E for steel is 29,000,000 lbs. in.) 

.000448; 12,992 lbs. per sq. in. 

(5) A steel bar, 10 inches long and of square section, 1 inch on 
the side when free, is under 40,000 pounds tension. What are its 
dimensions under this stress, which is within the elastic limit? 

10.0138 x. 99954 2 . 

(6) A copper rod of square cross-section, 2 inches on the side, 
and 5 feet long, stretches .0375 inches under a load of 40,000 
pounds. What is the modulus of elasticity, and what is the cross- 
section while the bar is under this stress? 

16,000,000 lbs. in.; 3.9983. 

(7) A one-inch square steel bar of 32,000 lbs. elastic limit is 
under a tension of 24,000 lbs.; what pressure per square inch on 
all of its sides will cause it to lengthen permanently? 12,000 lbs. 

(8) If a cube be subjected to equal tensions, or compressions, in 

each of the three directions normal to its opposite pairs of faces, 
what relation must exist between the stress of tension, or compres¬ 
sion, and the elastic limit of the material in order that the cube 
may be permanently strained? /> = 3<9. 

(9) The modulus of elasticity of copper being 16,000,000 
(lbs. in.), how much will the length and diameter of a round 
copper rod, 20 inches long and 3 inches in diameter when free, 
change under a tensile stress of 9000 lbs. per sq. in.? 

.01125 in.; .00056 in. 

(10) In order to bring to the vertical opposite walls which have 
fallen away from each other, round steel rods of 1 in. diameter 
are stretched from wall to wall and after being heated to 400° C. 
are set up taut. What pull will each rod exert when its tempera¬ 
ture has fallen to 200° C., supposing the walls not to have yielded 
at all? The coefficient of expansion of steel is .000011 for i° C. 

50,100 lbs. 

(11) How much would the steel rod of example (2), which is 

5277 ft. long when free, be increased in length by the stress due 
to its own weight? 1 9 -5& i n - 



174 


Naval Ordnance 


Section II.—Stress and Strain in Simple Hollow Cylinders. 

191. Consider a horizontal hollow cylinder, open at the ends, 
which are faced off in planes normal to the axis; and let this 
cylinder be filled with a fluid which is forced inward by two ex¬ 
panding plungers, the result being a uniform normal pressure 
upon the entire internal surface of the cylinder. Also let the entire 
outer cylinder surface be subjected to a fluid pressure. Then, the 
ends of the cylinder being free, and there being no longitudinal 
stress upon its walls, it is clear that the cylinder will remain a 
cylinder under the action of the pressures, and that each transverse 
section normal to the axis will remain a plane normal to the axis. 
Whatever shortening or lengthening of the cylinder may result 
from applying internal and external fluid pressure to it must be 



uniform over its whole cross-section; i. c., the longitudinal strain 
must, under the stated conditions, be constant throughout the 
cylindrical walls. 

192. Let 0 be any point (of radius r) within the walls of a 
cylinder (Fig. 29) whose inner and outer radii are R 0 and R,„ 
and which is subjected to internal and external pressures P 0 and 
P n respectively. Also let t, p and q be the circumferential, radial 
and longitudinal stresses, and e t , e p and e q the circumferential, 
radial and longitudinal strains, at the point O, E being the modu¬ 
lus of elasticity of the material. And let T 0 and T„ be the'cir¬ 
cumferential tensions at the inner and outer surfaces, or the values 
of t when r = R 0 and when r =R„. 

In the strained cylinder, the principal stresses at the point O are 
evidently the radial pressure p, which varies in value from P 0 at 



















Elastic Strength of Guns 


175 


the inner to P n at the outer surface; the circumferential tension t, 
which varies from T 0 at the inner to T n at the outer surface; and 
the longitudinal stress q, which is zero in the particular case con¬ 
sidered but which might be either tension or compression and 
either constant or variable. From equations (2), therefore, we 


obtain as the values of the principal strains, 



(a) 

1 

Ct ~ IT 

(--!)■ 

' 


(b) 

1 

e i>- E 

^ 1 co 
+ 


^(3) 

(c) 

II 

1 

hi]« 

(f - !)• 

> 



and since, under the stated conditions, e q is constant, we obtain 
from (c) above 


* t — p — constant — k. (4) 



Fig. 30. 


193. Considering any section of the cylinder (see Fig. 30) of 
unit length, if the cylinder is cut longitudinally by a diametral 
plane, the whole pressure acting outward upon the section is 
2P 0 R () , and the whole pressure acting inward upon the section is 
2 P„R n , so that the total force tending to burst the cylinder is 
2P 0 R 0 — 2P„R„. This force must be balanced by the total stress 
developed in the two sections of the cylinder walls, each of which 


is 


Rn 


Ru 


tdr. which total stress is 2 


Rn 

R 0 


tdr. f 


* It should be noted that this same result, t — p = constant, follows when 
q is constant as well as when q is zero. 

f We here assume the cylinder to be of unit length. 


































176 


Naval Ordnance 


194. Since we have equilibrium the disruptive forces and the 
resistance are equal, and we have 

" tdr=P 0 R 0 -P n R n . (5) 

J Rq 

Since this is true the general equation expressing the same 
thing must be true, or \tdr= — pr. But the differential of 

— pr is — pdr — rdp, .'. tdr— — pdr — rdp, 
from which we obtain 


t=- P -r d -t. 
‘ dr 


(6) 


From ( 4 ) we have t = p + k, and equating the two values of t 


we have p-\-k = — p — r~ , or 

dr 

2P + k=-r d / r . 

From ( 7 ) we obtain the expression - ^ ^ 

Integrating, 

= ~ \ d J> i log ( 2p k) — log i/r + log k x 

(k x being a constant of integration). 


\/ 2p + k= kl , 
1 r 


and the integration gives 


2p -f- k 


_ V 


(7) 


r - 


( 8 ) 


Substituting in ( 8 ) the value of k given in ( 4 ), we have 

2p + ‘~P= k - 


or 


k 2 

t + P=^- 


(9) 


195. Equations ( 4 ) and ( 9 ) express what are known as Lames 
Lazvs: * 


* As explained, these laws are only strictly true when the longitudinal 
stress is constant, or zero. 





Elastic Strength of Guns 


177 


1 . At any point whatever in a cylinder under fluid pressure the 
sum of the circumferential tension and the radial pressure varies 
inversely as the square of the radius. 

2 . The difference of the circumferential tension and the radial 
pressure is the same at all points. 

196. These, then, are the equations which express the relation 
between the circumferential tension and the radial pressure at all 
points within the cylinder walls : 

(a) t-p = k = T 0 -P 0 = T n -Pn, 

(b) (t + p)r* = k* = (T 0 +P 0 )R 0 2 = (T„ + P n )R, 2 . 

From tbe last part of equation ( 10 a) we obtain 



T n — T 0 — P 0 + P 


n> 


and from ( 10 b) we obtain 


J' _ ( ^0 + ^*0 )-^Q 2 _ P 

Rn 2 

Equating these values of T n , and clearing the equation, we 
obtain 

7 - p Rn~-\-Ro~ P 2Rn~ 

°~ n Rn 2 -R 0 2 n R„ 2 -R 0 2 ‘ 


197. From the first parts of equations ( 10 ), we have 

t — p = T 0 — P 0 , 
t + p= (•3 n o + ^°)^o~ # 

r 2 

By adding these two equations, we obtain 

2 t=(T,-P„)+ HslplEl , 

r 

and by subtraction we obtain 

2p — — ( T 0 -P 0 ) + (To _ + f ± l R Z . 


These expressions for t and p are in terms of T 0 and P 0 only. 
To make them general we substitute in them the value of T 0 found 
above, and reducing we have 


_P n R 0 2 -P„R,f RJR.ciP.-P,,) 1 
“ R,r-R 0 2 Rn 2 -R 0 2 r *• 

P Q R n 2 -P„Rn 2 , R 0 2 Rn 2 (Po-Pn ) I 
Rn 2 -R 0 2 Rn 2 -R „ 2 r 2 ’ 


13 













178 


Naval Ordnance 


and these equations enable us to determine the values of t and of 
p at any point. 

198 . Equations (3) give us general expressions for the strains 
in a cylinder in terms of t and p. But in this form the expressions 
are not available for use, for we desire them in terms of P 0 , P,„ 
R 0 and R„. 

To obtain the equations in this form we substitute for t and p 
in the equations (3) the values of these principal stresses as found 
in (11) and (12), which then reduce to the equations 


e t = -ft 


1^ 

E 


£]■ 03 ) 


€ v — t 


I 

E 


e 0 = -5 


1 

E 


2 P 0 R n *-P„R n * 4 R 0 2 R» 2 (P 0 -Pn ) 

3 Rn 2 -R 0 2 3 Rn 2 -R« 2 

2 P n R 0 2 -P n R n 2 4 R 0 a Rn*(P 0 -Pu) 11 

3 R n 2 — R 0 2 3 Rn 2 -R» 2 r* J* 

2 P n R n - P iiivbrl ^ T f \ 

3 Rn 2 -R,‘ J' U5; 


These are general equations and apply to all cases. 

The first two of these equations are the fundamental ones from 
which we shall deduce all the formulas used in our study of the 
elastic strength of guns. 

The greatest of the three strains given by (13), (14) and (15) 
for any point in the cylinder walls must not at any time exceed the 
elastic limit of strain of the material of the cylinder. That is, 
calling 6 the elastic limit of the material, as determined in a testing 
machine, the limiting value for each of the three strains et, e p and 

• 6 

Cq 1S E ' 

As et and e p denote the general values of the circumferential and 
radial strains (at any radius r ), we shall distinguish the values of 
the circumferential and radial strains at radius R 0 by et(R 0 ) and 
c p (R 0 ), and those at radius R n by Ct{R„) and e p {R„). 

199 . The quantities Ec t) Ee p and Ee q , respectively, equal in 
value the simple stresses which, acting alone, would cause the 
strains et, e p and e q , but these strains are actually caused by the 
concurrent action of the two stresses p and t. We shall hereafter 
designate Ee t , Ee p and Ee q as the true stresses, circumferential, 
radial and longitudinal respectively. 

A cylinder may be under stress in three ways, i. e., (1) interior 
pressure only; (2) exterior pressure only; and (3) both interior 
and exterior pressures simultaneously. 











Elastic Strength of Guns 


179 


The distribution of the true stresses throughout the walls of 
a simple cylinder under fluid pressure is best shown graphically, 
and we will therefore do this for the three cases; first, when the 
outer pressure (P„) is zero; second, when the inner pressure (P 0 ) 
is zero; and third, when both pressures act and P {) is greater than 
P„. In each case we assume a cylinder whose outer is three times 
its inner radius (R„ = ^R 0 ), so that its walls are a caliber thick. 

The series of equations that follow from this assumption are 
specific and hold only for the stated conditions. For other con¬ 
ditions of radii ratios we must go to equations (13), (14) and 
(15), substitute the given conditions therein, and deduce new 
equations which will of course be similar in form to those follow¬ 
ing in (16), (17) and (18), but will have different arithmetical 
figures. 

General equations covering the three specific conditions in Arts. 
200, 201 and 202 are deduced in Arts. 207, 209 and 211. 

200. Case I.—No exterior pressure. —Putting P n — o and R n ~ 
t,R 0 in (13), (14) and (15), we obtain as the values of the true 
stresses: 


(a) Ec t — 

(b) Ee p = 

(c) Ee q - 




l SPnA 

r 2 /’ 

i8P 0 2 ^ 



(16) 


From these it will be seen that as r increases from R 0 to R n the 

circumferential true stress diminishes from P 0 to P 0 , its 

12 I — 

value midway, where r = 2R 0 , being -^-P 0 ; the radial true stress 

24 

17 I 

diminishes (algebraically it increases) from — — P 0 to— ~P 0 > 


its value midway being 



while the longitudinal true stress 


has the constant value — ~ P 0 throughout the cylinder wall. Fig. 

31 illustrates the distribution of the tangential and radial true 
stresses, the former on the right and the latter on the left of the 
section, the ordinates above the horizontal diameter indicating 






i8o 


Naval Ordnance 


tensions and those below it indicating compressions. 1 he figures 
on the inner, middle and outer ordinates are the true stresses in 
tons per square inch which would result from an internal pressure 
of 12 tons per square inch. 



201 . Case II.—No interior pressure.—Putting P„ = o and R„ = 

3 R 0 in (13), (14) and (15), we obtain as the values of the true 
stresses: 


(a) 

(b) 

(c) 



- 07 ) 


J 


From these it will be seen that as r increases from R 0 to R„, the 
circumferential true stress diminishes (algebraically it increases) 

from — — Pn to —— P n , its value midway, where r = 2R 0 , being 
4 12 


9 

8 


P n ; the radial true stress diminishes from + 


3 

4 


Pn tO 


/ 


12 



its midway value being — § P n ; while the longitudinal true stress 
has the constant value 4-f Pn. Fig. 32 illustrates this, the right- 
hand curve showing the tangential and the left-hand curve the 
radial true stress at each point in the wall thickness, ordinates 
above the horizontal diameter indicating tensions and those below 
it indicating compressions. The figures on the inner, middle and 









Elastic Strength of Guns 


iSi 


outei ordinates are the true stresses in tons per square inch which 
would result from an external pressure of 12 tons per square inch. 



202 . Case III.—Exterior pressure one-half the interior pres¬ 
sure.—Putting P n = ^P a and /v , „ = 3/? n in (13), (14) and (15), we 
obtain as the values of the true stresses: 


(a) £*•= + £» (18^-7). 

(b) £«,= -&( 18^+7), 

(c) Ee q — ~-P 0 . 


kis) 


From these it will be seen that as r increases from R n to R n the 

circumferential true stress diminishes from — P n to — ^ P n , its 

24 24 


value midway being — ^ P 0 ; the radial true stress diminishes 

4 ° 

(algebraically it increases) from — z$. P 0 to — P 0 , its value 

midway being — ^~-P 0 while the longitudinal true stress has the 
4o 

constant value -1—— P n . Fig- 33 illustrates the distribution of 

24 

the tangential and radial true stresses, the former on the right and 
the latter on the left of the section, the ordinates above the longi- 








I §2 


Naval Ordnance 


tudinal diameter indicating tensions and those below it indicating 
compressions. The figures on the inner, middle and outer ordi¬ 
nates are the true stresses in tons per square inch which would 
result from an internal pressure of 12 tons per square inch and an 
external pressure of 6 tons per square inch. 



203 . Comparing Fig. 33 with Figs. 31 and 32, it will be seen 
that the ordinates of the curves in the former are the algebraic 
sums of the corresponding ordinates of Fig. 31 and half those of 
Fig. 32; the stresses due to 12 tons internal and 6 tons external 
pressure acting together are the same as the algebraic sums of the 
stresses due to the same pressures acting separately. 

204 . The strains given by equations (13), (14) and (15) are 
changes of length per unit length, and since e p is the radial strain. 
CpXdr is the change of length of dr, and so the whole change of 


thickness of the cylinder wall is 



e p dr. 


Also et is the change of length per unit length circumferentially 
and therefore in a cylinder the change in the length at any circum¬ 
ference will be the length of the circumference multiplied by the 
change of length per unit length. That is, if Ac is the total change 
in the length of any circumference of length C, then 


Ac = C • e t . 


If r is the radius of the circumference, then C = 2 tri', and sub¬ 
stituting this value for C above, we have 

Ac = 2ttY • et. 




Elastic Strength of Guns 


183 


But we also know that \c — 2tt • A r, where A r is- the change in 
the radius r due to the change in the circumference C caused by 
Ac. Equating these two values of A c, we have 

2 it • \)' = 2irr • Ctj 
or 

A r = r • e t , 

which means that the change of radius at anv point whose radius 
is r must be r • et. 

Therefore the change of the outer radius is R„ ■ e t (R„), and the 
change in the inner radius is R 0 • et(R 0 ) , and the difference be¬ 
tween the change in the outer radius and the change in the inner 
radius must be equal to the whole change of thickness, i. e., 

Whole change of thickness = R n • ct(R n ) —R n • et(R n )- 

But we have an integral expression for the change of thickness, 
and these two expressions must therefore be equal; therefore 
m R 

" e p dr=R n e t (R„)-R 0 e t (R 0 ), 

R 0 

and it will be found upon trial that this is true of the values of 
e p and et given by (13) and (14). 

205 . The hypothesis made in Art. 191 that there is no longi¬ 
tudinal stress is, of course, not true, as a rule, for actual con¬ 
structions. In the built-up guns, for example, whose strength we 
are investigating, one end of the bore is closed by a breech block 
which sustains the internal pressure and thus causes a total longi¬ 
tudinal stress ttR 0 2 P 0 which is distributed over the cross-section 
of one or more of the cylinders of which the gun is composed. 
This stress may be taken account of by assuming that it is uni¬ 
formly distributed, but, as will be shown further on, the hypothesis 
that q is zero accords as well or better with the facts than any 
other available one. 

Examples. 

(1) Show that in an infinitely thick hollow cylinder ( R n = cc ) 
subjected only to internal pressure (F 0 ) the true circumferential 
and radial stresses at the inner surface are of equal value but 
opposite sign. What are their values? What is the value of the 
longitudinal stress ? 


+|E 0 ; -i p o ;o- 



184 


Naval Ordnance 


(2) What are the true stresses at the inner surface of an 
infinitely thick hollow cylinder subjected only to external pressure 

CP.)? 

— 2P n + 3 P n + %P n ■ 

(3) If the external and internal pressures are equal, what is 
the state of stress in the cylinder walls? 

Ee t =Ee,= -%P 0 ; Ee q =+tP 0 . 


(4) What would be the change of thickness of a hollow cylinder 
one diameter thick under internal pressure alone? 

_5 PoK 

6 E - 


(5) What would be the change of thickness of a hollow cylinder 
one diameter thick under external pressure only ? 


P nP 0 

2 E 


(6) A hollow cylinder half a caliber thick is subjected to an 
internal pressure of 6 tons per square inch. What is the greatest 
true stress resulting and where does it occur? What are the true 
stresses at the outer surface? 

Ec t (R 0 ) = 12 tons per sq. in. 

Eet(Rn)- 4; Ec p (R n ) = -ii; Ee q = - 1^. 


(7) If the cylinder of example (6) is only one-quarter of a 
caliber thick, what are the true stresses at inner and outer sur¬ 
faces ? 

Ee t (R 0 ) = 17!; Ee p (R 0 ) =-nl-\ . 

Eet(Rn) = 9 §; Ee p (R n ) = - 3 iJ 3s ' 

(8) Show that, as the thickness of wall of a cylinder under 
internal pressure is made a smaller and smaller fraction of its 
inner diameter, the circumferential stress becomes more and more 
nearly constant throughout the wall. If the circumferential stress 
were constant, what would be the relation between it and the 
internal pressure ? 

p _ Pn R 0 r p 

°~ R 

(9) A hollow steel tube, radii 3 in. and 6 in., is subjected to an 
internal pressure of 13 tons per sq. in. Determine the three prin¬ 
cipal strains at the inner surface. What is the least elastic limit 




Elastic Strength of Guns 


185 

of the steel which will permit the application of such a pressure 
without permanent set ? 

et(R 0) =.002; c p (R u ) = —.00156; c q — —.00022. 

26 tons per scp in. 

(10) With the data of example (9) determine the three princi¬ 
pal strains at the outer surface of the tube. 

Ct(R n ) =.00067; c p (R„) = — .00022 ; c q — — .00022. 

(11) Show that the change of wall thickness of a cylinder is 
independent of the value of the external pressure in the case 
where the outer radius is twice the inner radius. 

Change = — . 

3E 


Section III.—The Elastic Strength of Simple Hollow 

Cylinders. 


206 . We will denote the elastic limit under tension of the 
material of the cylinder by 6 and its elastic limit under compres¬ 
sion by p. In the case of the forged steel used in modern gun 
construction, these elastic limits are usually taken to be equal, but 
with some materials, notably cast iron, p is considerably greater 
than 6 , and even in the case of steel it is probable that p is always 
somewhat greater than 6 . 

In accordance with the principle stated in 188, we consider that 
the limit of safety is reached whenever either of the principal 
strains, circumferential, radial or longitudinal, attains the value 

Q 

in extension or the value -g in compression; in either case we 

suppose that the strain ceases to be wholly elastic, and though 
rupture may not follow, some permanent change of dimensions 
or distortion will result. 

In order, therefore, to determine the maximum pressure which 
a given cylinder will withstand without permanent set, we have 
only to equate the greatest strain of extension which results from 


6 

pressure to -g-and the greatest strain of compression to 


and the least of the pressures given by solving these two equations 
is the greatest pressure which the cylinder can safely be subjected 
to. In other words, the limit of the elastic strength of the cylinder 



Naval Ordnance 


i 86 


is reached when either the greatest true stress of tension equals 
the elastic limit of the material under simple tension, or the 
greatest true stress of compression equal the elastic limit of the 
material under simple compression. In accordance with Art. 199. 
we have three cases. 

207 . Case I.—Internal pressures only.—Putting P n — o in 
(13), we obtain 



This expression is obtained from equation (13) exactly as equa¬ 
tion (16a) is obtained, except that no assumption regarding the 
ratio between R n and R 0 has been made and hence it is a General 
Equation for this particular case (t. c., no external pressure). 
[If we substitute in equation (19) the ratio between R„ and R 0 
assumed in Art. 199 we will obtain equation (16a), and, similarly, 
from 199 we can obtain (16b).] Equation (19) is always plus, 
showing that the circumferential true stress in this case is always 
tension; and its greatest value is when r has its least value R n . 
This shows that the greatest stress will be at the inner surface 
(weakest point) and this maximum stress must not exceed 6 . 

Hence we find the value of P n which will make the greatest 
circumferential true stress equal the elastic limit of the material by 
putting Ect — Q and r = R 0 in (19). This gives 


from which 


6 s(R n 2 -R 0 2 ) ( R »~ + 2Rn ~'>’ 

n _ 3(Rr 2 -R,r) a 
°~ 4 RS + 2R* 


(20) 


This expression, having been deduced from equation (13), gives 
the value of P n that will bring the cylinder to its elastic limit of 
circumferential strain. 

We must also find the value of P 0 that will bring the cylinder 
to its elastic limit of radial strain. 

Hence, putting P„ = o in (14), we obtain 


Ee _ /. 


(2l) 


This is always negative, showing that the radial true stress in 
this case is always compression; and its greatest value (numeri- 






Elastic Strength of Guns 


187 


cally) is when r = R 0 . Hence we find the value of P n which will 
make the greatest radial true stress equal the elastic limit of the 
material by putting Ee,,= — p and r=R 0 in (21). This gives 

2 P n 


P 


P 3 (Rn 2 ~R 0 *) 

3 (Rn’-R/) 

4 R„ 2 -2R 0 - 


(R 0 '~- 2 R,r), 


(22) 


The determination of the value of the longitudinal true stress is 
unnecessary, since it can never exceed, and in all practical cases is 
much less than, one or the other of the other two principal true 
stresses, the circumferential and the radial. 

Now, comparing (20) and (22), since p is always equal to or 
greater than 6 , and since the denominator of (20) is greater than 
the denominator of (22), the value of P 0 given by (20) will 
always be less than the value of P n given by (22). When P 0 
reaches the value given by (20), the elastic limit of strain is 
reached circumferentially, and further increase of P 0 is inad¬ 
missible. 

Consequently the maximum internal pressure allowable in the 
case of a simple hollow cylinder under no exterior pressure is 
given by 



3 (R n 2 -R„ 2 ) 

4 Rn Z + 2R n ~ 


0 , 


(20 bis ) 


in which 6 is the elastic limit of the material under tension. 

Evidently equation (20) gives not only the relation between the 
maximum allowable internal pressure and the elastic limit of the 
material, but equally the relation between any internal pressure 
and the greatest resulting true stress (within the elastic limit). 

If any three of the four values 6 , R n , P 0 and R n be given, (20) 
may be solved for the fourth value. For example, given all ex¬ 
cept R„, then 


R n — R 0 


I sd+2P n 
\ 30-4PO ’ 


That is, by means of (20) the necessary thickness of a cylinder 
to safely withstand a given internal pressure is readily determined. 
Writing equation (20) in the form 


Po = 3(Rn 2 -Rp 2 ) 

6 ^R n ~-\r^Rp 2 






Naval Ordnance 


i 88 


and assuming either ratios between the radii to get corresponding 
ratios between P 0 and 9 , or vice versa, we can plot a curve show¬ 
ing the proportions that must exist between R n and R 0 for any 
given proportion between P 0 and 6 , as shown in Fig. 34. 

J ^ 

As an example, assuming first that jf 1 — 1 > we see that there is no 

P 

cylinder and hence-^=0. Again, when R,,= cc, we have 

6 



but R n = sc, therefore 


_ 30 -°) _a 

9 4 + 0 4 ' 


B 

8 



attaining the maximum value f when =00, and clearly indi- 

* .° 

cates the small effect upon strength of increasing wall thickness 
beyond a caliber, that is, when = wall thickness is 

2 ,R 0 — R 0 = 2R 0 — d— 1 caliber. 

208 . Examples. — (1) What is the limiting value of the in¬ 
ternal pressure which any simple cylinder (regardless of its thick¬ 
ness) will stand without permanent set, the elastic limit of its 
material being 6 ? % 6 . 

(2) The walls of a 6-inch steel shell are 1.5 in. thick; if the 
tensile strength of the steel is 50 tons per sq. in., what powder 
pressure will burst the shell? 25 tons per sq. in. 













Elastic Strength of Guns 


189 


(3) What internal pressure will produce a circumferential elon¬ 

gation of .0015 in the case of a simple steel tube of 3 in. interior 
and 6 in. exterior radius? 9.75 tons per sq. in. 

(4) What internal pressure will a cast-steel cylinder of 4 in. 

internal and 6 in. external radius stand within its elastic limit of 
30,000 lbs. per sq. in.? 10,227 lbs. per sq. in. 

(5) A nickel-steel cylinder of 7 in. interior radius and 0.5 in. 

wall thickness has an elastic limit of 70,000 lbs. per sq. in. What 
internal pressure will it withstand? 4713 lbs. per sq. in. 

(6) A cylinder of 7 in. interior diameter has walls 3.5 inches 
thick. If its elastic limit is 36,000 lbs. per sq. in., what internal 
pressure will it stand? How much pressure could it withstand if 
its wall thickness were doubled ? if trebled ? 

18,000; 22,740; 24,550 lbs. per sq. in. 

(7) Determine the proper thickness for a cylinder of 6 in. 

inner radius which is to stand an internal pressure of 3000 lbs. 
per sq. in., the elastic limit of the material being 28,000 lbs. per 
sq. in. 0.708 in. 

(8) If the radii are 8 in. and 9 in. and the elastic limit is 
60,000 lbs. per sq. in., what is the maximum allowable internal 
pressure? What would it be if the circumferential stress were 
constant throughout the cylinder walls? 

6770; 7500 lbs. per sq. in. 

(9) What thickness should a cylinder of 4 in. interior radius 

have to withstand an internal pressure of 8000 lbs. per sq. in., if 
the elastic limit is 40,000 lbs. per sq. in. ? 0.973 bi. 

(10) What internal pressure will a cylinder of 6 in. interior 

radius and 4 in. wall thickness withstand, if the elastic limit is 18 
tons per sq. in.? 7.32 tons per sq. in. 

209. Case II. — External pressure only.—Putting P„ = o in 
(13), we obtain 



in the same way that (19) is obtained, and is a General liquation 

* Equations (23) and (25) being General Equations, if ratios between 
R„ and Ro as assumed in Art. 199 are substituted therein, the specific equa¬ 
tions (17a) and (17b) respectively will result. 



Naval Ordnance 


lyo 


for this case. This is always negative, showing that the circumfer¬ 
ential true stress in this case is always compression; and its great¬ 
est value is when r = R„. Hence we find the value of P„ which 
will make the greatest circumferential true stress equal to the 
elastic limit of the material by putting Eet=—p and r = R 0 in 
(23). This gives 



(24) 


This expression, having been deduced from equation (13), 
gives the value of P 0 that will bring the cylinder to its elastic 
limit of circumferential strain. As in the previous case we must 
also find the value of P 0 that will bring the cylinder to its elastic 
limit of radial strain. 

Hence, putting P 0 = o in (14), we obtain 



Equation (25) is positive when r = R 0 and continues so until r 
attains the value R 0 V 2, beyond which point it becomes negative; 
its greatest numerical value, however, is when r = R 0 . Hence, to 
find the value of P„ which would make the greatest radial true 
stress equal the elastic limit of the material, we would put 
Ec „=0 and r = R 0 in (25). A comparison of (25) with (23), 
however, will show that, for every value of r, Eet is greater than 
Ec,>, so that the elastic strength of the cylinder depends upon its 
resistance to circumferential stress and not upon its resistance to 
radial stress.f 

Consequently the maximum external pressure allowable in the 
case of a simple hollow cylinder under no interior pressure is given 


by 



(24 bis) 


in which p is the elastic limit of the material under compression. 

* See footnote, page 189. 

t With a material like cast iron, of which the elastic limit of com¬ 
pression greatly exceeds that of tension, the limit of elastic strain radi¬ 
ally (in this case extension) may in some cases be reached before the 
limit of elastic strain circumferentially (in this case compression) is 
attained. 






Elastic Strength of Guns 


191 

Fig- 35 shows the increase of the ratio as wall thickness 

P 

increases, and clearly indicates how little is gained by going be¬ 
yond a thickness of one caliber. 

This curve is plotted from equation (24) in the same way Fig. 
34 is obtained from (20). 

Of course (24) expresses the relation between the external 
pressure and the greatest resulting true stress within as well as at 
the limit of elastic strain. 


In 

p 



210. Examples. — (1) What is the limiting value of the ex¬ 
ternal pressure which any simple hollow cylinder, regardless of its 
thickness, can withstand without permanent set, the elastic limit 
of compression being p ? \p. 

(2) What external pressure can a tube of 7.5 in. interior radius 
and 1.75 in. thickness of wall withstand, the elastic limit for 
compression being 30.000 lbs. per sq. in.? 5*39 lbs. per sq. in. 

(3) How thick should the tube of example (2) (R,, — "/.5 in.) 
be to withstand an external pressure of 10,000 lbs. per sq. in.? 

5.49 in. 

(4) The inner and outer radii of a steel tube are 4 in. and 7 in., 
and it is to be subjected to an external pressure of 8.3 tons per 
sq. in. What are the circumferential and radial strains at the 
inner surface? What is the greatest true stress? 

— .001897; + .000632; 24.65 tons per sq. in. 

(5) How thick should the walls of a 6-inch shell be to with¬ 

stand 6 tons per sq. in. external pressure, without passing the 
elastic limit of compression of 18 tons per sq. in. 1.27 in. 

(6) What external pressure will a cylinder of 6 in. interior 

radius and 4 in. wall thickness withstand, if the elastic limit is 18 
tons per sq. in. ? 5.76 tons per sq. in. 






192 


Naval Ordnance 


(7) What wall thickness should a cylinder have to withstand 
8000 lbs. per sq. in. external pressure, the interior radius being 
4 in. and the elastic limit 40,000 lbs. per sq. in. ? 1.16 in. 

• (8) If the interior radius is 8 in., the wall thickness 1 in., and 
the elastic limit 60,000 lbs. per sq. in., what is the maximum allow¬ 
able external pressure? What would it be if the circumferential 
stress were constant throughout the walls? 

6297; 6667 lbs. per sq. in. 

211 . Case III. —Both internal and external pressure.—In this 
case there are two main subdivisions; (a) when the exterior 
pressure exceeds the interior pressure, and (b) when the interior 
pressure exceeds the exterior. 

Furthermore, there are two subdivisions under (b), making a 
total of three possible solutions. 

In Art. 202 the expressions deduced are for a specific case, with 
definite ratios of radii. Here we deduce General Expressions, 
whereas equations (18) a, b and c are specific for the conditions 
stated in Art. 202. Which of the true stresses first reaches the 
elastic limit depends, in this case, upon the relation between the 
two pressures, and we must consider the three possible cases 
separately. 

(a) We first consider the case where 

P n >P 0) hence P n Rn>P p R 2 . 

Looking at (13), since P n Rn 2 is greater than P 0 R n ~ we see at 
once that both terms of (13) are negative, showing that the cir- 
circumferential true stress is always compression; and its greatest 
numerical value is when r has its least value R 0 . On the other 
hand, the two terms of the value of Ee p , equation (14), have oppo¬ 
site signs, showing that the radial true stress may be either tension 
or compression, according to which term preponderates, and also 
showing that at each point Eet is greater numerically than Ee p . 
We therefore obtain an equation between the value of P 0 and P„ 
which will, make the greatest true stress resulting from their con¬ 
current action equal the elastic limit of the material by putting 
Eet — — f) ( — p because, as we found above, the terms will be nega¬ 
tive, showing the stress to be compressive) and r = R 0 in (13) 
This gives 

_ 6 P„R,r- 2 P 0 RG-- 4 P»R>r 

p 3 

p _ 6P„R„*-T,(R,r-R 0 2 )p 

4RS + 2R 2 


(26) 




Elastic Strength of Guns 


193 


Consequently, zvhen P n exceeds P 0 , the relation between the 
internal pressure and the maximum allowable external pressure is 
given by (26), in which p is the elastic limit under compression, 
(b) We next consider the case where 


P 0 >P n but P lt R 0 2 <P„R n 2 . 


P 0 R 0 ~ is less than P„R n 2 owing to the fact that P 0 is not great 
enough to overcome the excess of R, 2 over P 0 2 . 

In this case the first term of the value of Eet, equation (13), 
remains negative, while the second term is positive, so that the cir¬ 
cumferential true stress may be either tension or compression, 
according to which term preponderates. But both terms of the 
value of Ec p , equation (14), are now negative, showing that the 
radial true stress is always compression and is numerically greater 
than Eet at each point; moreover, the maximum numerical value 
of Ec p is when r has its least value R 0 . We therefore obtain an 
equation between the values of P 0 and P n which will make the 
greatest true stress resulting from their concurrent action equal 
to the elastic limit of the material by putting Ee p — —p and r = R 0 
in (14). This gives 


_P n (4R„ 2 -2R n 2 )-2P n R „ 2 

P 3(Rn 2 -R 0 2 ) 

ft- 3(Rn 2 -R« 2 )p + 2P„R, 2 
4Rn 2 + 2R 0 2 


( 27 ) 


Consequently, when P 0 exceeds P n but at the same time P 0 R ( 2 
is less than P„R, 2 , the maximum allowable internal pressure is 
given by (27), in which p is the elastic limit of the material under 
compression. 

(c) Lastly, we consider the case where 


P 0 >P n and P 0 R 0 2 >P„R, 2 . 


Here P 0 is great enough, together with R 0 2 , to overcome the 
excess of R n 2 over R 2 . 

In this case both terms of the value of Ee t , equation (13), are 
positive, showing that the circumferential true stress is always 
tension; its greatest value occurs when r = R 0 ; and at each point 
it is numerically greater than Ee p since the two terms which make 
up the latter’s value are now of different signs. That is, Ee t from 
equation (13) is numerically greater than Ec p from equation (14) 


14 




194 


Naval Ordnance 


if the same internal pressure, P 0 , is used in both equations. There¬ 
fore a smaller P 0 is required to produce a circumferential true 
stress, 0 , in equation (13), than is required to produce a radial 
true stress, p, in equation (14) equal to or greater than 6 . We 
therefore obtain an equation between the value of P t) and P n 
which will make the greatest true stress resulting from their con¬ 
current action equal the elastic limit of the material by putting 
Eet — 6 and r = R 0 in (13). This gives 

p_P n (4Rn 2 + 2 R 0 2 )- 6 P„R,r 
3(R n 2 — R 0 -) 

P — S(Rn~ — R n ')G + ()P„R„- (28) 

° 4 Rn 2 + 2R 0 * * V 



Consequently, when P 0 exceeds P„ and at the same time P 0 R 0 2 
exceeds P n Rn 2 , the maximum allowable internal pressure is given 
by (28), in which (9 is the elastic limit of the material under 
tension. 

Of course equations (26), (27) and (28), each under its appro¬ 
priate conditions, express the relation between the internal pres¬ 
sure, the external pressure and the greatest resulting true stress 
within the elastic limit as well as at that limit. 







Elastic Strength of Guns 


195 


212 . The relation between simultaneous values of P 0 and P n 
which will just bring a given cylinder to the limit of its elastic 
strength may be graphically shown by drawing the three straight 
lines represented by equations (26),. (27) and (28). In Fig. 36, 
values of P 0 are represented by the ordinates, and corresponding 
values of P„ by the abscissae, and the cases of five different thick¬ 
nesses of cylinder wall are illustrated. 

213 . Taking equation (26), which is the expression of Case 
Ilia, and assuming now a radii ratio R K = 2 R 0 we find (26) re¬ 
duces to the form 


p _ 24P„ —9 

0 18 * 


(a) 


which is a simple equation between simultaneous values of P n and 
P 0 for the assumed radii ratio. 

Case Ilia is based on the fact that P rt >P 0 * Hence, putting 
P 0 — o in the equation above we find P„ = fp, which point we plot. 

Now, as Case Ilia approaches Case Illb, that is, as P n and P 0 
become more and more nearly equal, we approach a point where 
P„ will be equal to P 0 and from this point P 0 will begin to be 
greater than P n and we will have the condition of Case Illb. 
Therefore the transition point between Case Ilia and Case Illb 
occurs when P n = P 0 . 

Hence, substituting P 0 = P n in equation (a) above, we find 

i 8 P n = 24 P n - 9 p, 
or 

P — P * 

* r\ — o p — r 0. 

We plot this point and, as equation (a) evidently expresses a 
straight line, by joining the two points (t. c., P 0 = o, P„ = §p; and 
P n z=P 0 = % p ) we have the graph showing the simultaneous values 
between P„ and P 0 when R n = 2 R 0 . 

Case Illb states that P 0 >P n , but P 0 must begin to be greater 
than P n from a point where P n = P 0 . But the point P n = P 0 = %p 
is the transition point from Case Ilia to Case Illb. Hence, first 
substituting in equation (27) the assumed radii ratios, we find 
(27) reduces to 

+ (b) 


* Although the point P n = Po=2P is here determined for the condition 
Rn = 2R0, it will be found that this point will be the same for all radii ratios. 




196 


Naval Ordnance 


which is a simple equation between simultaneous values of P n and 
P n for the assumed radii ratio. 

We must plot the graph of this equation from the point where 
P n = P 0> { . e., the transition point from Case Ilia to Case Illb. 
Therefore, substituting P„ = P 0 in equation (b) above, we find 


Pn 


Po = 


9 p 4 - &P 0 
14 


or 


p 0 =y=p n , 


which we see is exactly the same value given for the graph 
equation (26) and consequently Case Illb is a direct continua¬ 
tion of Case Ilia. 

Now as P n decreases we approach the condition of a cylinder 
under interior pressure only, which is the condition of Case I 
given in Art. 207, and we know from that article that P 0 cannot 
exceed f 6 when P n = o even if R„ = 00. 

P n in Case Illb will not be zero, but it may be very small, so we 
may safely substitute F 0 = -|6 I in equation (b) to see how large P n 
must be owing to the fact that R„ does not equal 00, but the 
definite value 2R 0 . 

Therefore, substituting P 0 = f# and remembering that 0 = p (for 
steel) in equation (b), we find P n = ^ s p. 

We plot the two points (i. e., P n = P 0 = §p; and P o = f 0 , P n = T \p) 
and knowing from its form that equation (b) is a straight line, 
by joining the points we have a graph of Case Illb. 

Now we see that in equation (28) when P n attains the value 


has the value % 6 , regardless of the thickness of the 


3 ^ q 2 0 p 

4 Rn 2 ’ ° 

cylinder, and with these values of the pressures the inner surface 
of the cylinder is both at its elastic limit of extension circum¬ 
ferentially and at its elastic limit of compression radially. 

Further increase of P 0 is allowable if P„ be also increased, but 
from the point where P o = ^0 the relation between _P 0 and P n is 
given by (27), and hence this value of P 0 = f (9 is the transition 
point (or line in this case) between Case Illb and Case I lie. 

We therefore now take equation (28) and first substitute our 
assumed radii ratios, reducing equation (28) to the form 


r> _90 + 24 P» 
0 18 


(c) 



Elastic Strength of Guns 


197 


which is a simple equation between simultaneous values of P„ and 
P 0 for the assumed radii ratios. 

Starting with the value of P n = f0, the transition value, we find 
P n = TS^ = t%P> (0 = p) an( J this is the same point at which we found 
equation (27) to terminate on the P n — %6 line, and hence Case 
IIIc meets and is a direct continuation of Case 111 b. 

Again substituting P„ = o in equation (c) we find P o = b 0 , and 
as equation (c) expresses a straight line we join the two points 
(i. e., P o = f 0 , P„ = ^\rp ; and P 0 =hO. P„ = o) which gives the graph 
of Case Illb. 

214 . Fig. 36 shows the graphs obtained from equations (26). 
(27) and (28) for the radii ratios assumed above, and for four 
other ratios, these being drawn in the same way as the example 
taken (/. e., for R n = 2R (t ), not that these five relations are the 
only ones possible but that they are simply five examples here 
shown. 

The relative values of P 0 (ordinates) and P„ (abscissae) are 
plotted to scale. Therefore, given any value of P 0 or P„. the 
equations that should be used to find P„ or P 0 are indicated. 

215 . Cases I, II and the subdivisions under Case III are all 
applicable to a built-up gun simultaneously. 

The outer layer of a gun is always under the stresses shown by 
equation (19), both at rest and in action. The inner tube of the 
gun is under the stress of Case II, equation (23), in the state of 
rest. The layers of the gun intermediate between the tube and 
the outer layer are under the stresses of the three subdivisions of 
Case III, as is the tube in the state of action. Which one of the 
subdivisions of Case III to use depends upon the relations between 
P„ and P 0 and the radii ratios. 

(26) represents the greatest value of P„ while P 0 is reduced 
in value. 

(27) represents the relation between P„ and P„ as we go beyond 
the value §6 for P 0 . 

(28) represents the relation between P„ and P 0 as long as P„ 
is 1 6 or less. 

In one case only are all three equations used and that is when 
P 0 has the value f 6 . In this case the conditions of all three equa¬ 
tions are fulfilled but as would be expected we find the values 
derived from (27) and (28) are the same. 


198 


Naval Ordnance 


An example or two will suffice to complete the explanation. 
Suppose we take example 2, Art. 216. here P„—p. From what 
has been said before and by looking at Fig. 36 we see that a line 
erected parallel to the ordinate from a point on the abscissae cuts 
both (27) and (26) ; we have the two values and from what has 
gone before we would expect the maximum value of P 0 to come 
from (27) and the minimum from (26). 

Example 5, Art. 216: — = A 000 - or p — \. 

b 30000 

Here we find that our line cuts (28) and (27) ; but as the two 
relations are not the same. P„ is not increased so P n is not in¬ 
creased, (28) is our only solution. 

Example 6, Art. 216: = 10000 _i Our line this time 

r 0 70000 

parallel to the abscissae cuts only (26). 

17 I A . s P 0 20000 _ 5 

Example 7. Art. 216: - &• 

r b 36000 

Our line parallel to the abscissa cuts both (26) and (28), hence 
there are two solutions and two external pressures. 

216 . Examples.— (1) If P„ = 2P 0 and P n = p = b, what is the 
greatest and what the least allowable value of P n ? 


17 . 5 

— P , p- 

14 6 r 

(2) If R n =-^-R 0 and P n =p, what are the greatest and least 

4 

allowable values of P n ? 


77 . 4i 

68 p ’ 44^' 

(3) If R n = -~R 0 , what value must P„ have in order that P 0 may 


__3 
1 2 

have the value of $ 6 ? 


1 ,, 8 a 

— 6 or — 6 . 

3 9 

(4) If R„ = ^-R 0 , what value must P n have in order that P 0 may 
4 


_ 5 

i — 

4 

have the value f 6 ? 


12 a 21 a 
6 or — 6 . 

25 25 

(5) What internal pressure will a cast-steel cylinder of 4 in. 
interior and 6 in. exterior radius stand within its elastic limit of 



Elastic Strength of Guns 


199 


30.000 lbs. per sq. in. if it is under an external pressure of 5000 lbs. 
per sq. in. ? 16.363 lbs. per sq. in. 

(6) A nickel-steel cylinder of 7 in. interior radius and 1.5 in. 

wall thickness has an elastic limit of 70,000 lbs. per sq. in. What 
external pressure will it withstand it* it is under an internal pres¬ 
sure of 10,000 lbs. per sq. in. ? 20,190 lbs. per sq. in. 

(7) The inner and outer radii of a steel tube are 4 in. and 7 in.; 

what external pressure will enable it to withstand an internal pres¬ 
sure of 20,000 lbs. per sq. in. if the elastic limit of the steel is 
36,000 lbs. per sq. in. ? 3390 to 27,630 lbs. per sq. in. 

Section IV. —The Elastic Strength of Compound Cylinders. 

217 . A reference to Fig. 31 will show that the outer portions of 
a thick simple cylinder play but a small part in resisting internal 
pressure. A compound cylinder is one formed by the super¬ 
position of simple cylinders, the object being to utilize to the 
utmost the contractile power of the outer parts and thus to in¬ 
crease the resistance to internal pressure beyond what it would be 
if the entire mass were in one piece. 

If the elementary cylinders are of the same material, or have 
equal moduli of elasticity, they must be assembled so that each 
exerts an initial pressure upon the one within it. This is accom¬ 
plished by making the interior diameter of each elementary cylin¬ 
der (before it is put in place) less than the exterior diameter of 
the cylinder upon which it is to be superposed by a certain 
quantity which is called the shrinkage. A compound cylinder so 
assembled is said to be under initial tension. 

If the elementary cylinders are of different materials, and are 
so arranged that the modulus of elasticity of each is greater 
than that of the one within it, they may be assembled without 
shrinkage. Such a cylinder is called a compound cylinder of 
variable elasticity* 

* Modulus of elasticity is inversely proportional to the elasticity or 

allowable strain, for E = — , or E is inversely proportional to e. For 

e 

example, if we have two cubes, one rubber and one steel, and on each we 
place equal heavy weights, the strains in the rubber will be greater than in 

the steel though both are under the same stress; therefore the fraction £- 

is much smaller for rubber (e being greater) than for steel and hence the 
E’s vary inversely as the c’s. Thus we see why the most elastic material 
must be placed next to the bore. 


200 


Naval Ordnance 


These two principles of variable elasticity and of initial tension 
were formerly often employed in combination, the commonest 
examples being cast-iron guns with reinforcing hoops of steel, but 
in modern gun construction, excepting for certain bronze field 
pieces, steel is now used to the exclusion of other metals, and the 
principle of initial tension is universally adopted.* 

218 . In the investigation of the elastic strength of a compound 
cylinder, it is necessary to consider its state of strain both when 
the maximum internal pressure is acting and when the internal 
pressure is zero: the first of these two conditions is called the state 
of action and the second is called the state of rest. 

In the state of action each cylinder except the outer one is sub¬ 
jected to two pressures, one internal and the other external, while 
the outer cylinder is subjected to internal pressure only, atmos¬ 
pheric pressure being neglected on account of its insignificant 
value as compared with the other forces. 

In the state of rest the inner cylinder is under external pressure 
only, the outer cylinder is under internal pressure only, and each 
of the intermediate cylinders is subjected to both an internal and 
an external pressure. 

219 . We adopt the following nomenclature: 

R 0 and R 1 are the inner and outer radii of the innermost or first 

elementary cylinder, R t and R 2 of the next.. and R„ of 

the outermost or ?jth. 

6 0 and p 0 , 6 1 and p x , . . . . 6 n and p„ are the elastic limits of the 
material of the elementary cylinders in the same order, from the 
ist to the nth ; and E is their common modulus of elasticity. 

P 0 , P l , . .. .P n are the radial stresses in the state of action at 
the successive surfaces of the elementary cylinders, and P 0 , P lf 
... .P„ are the radial stresses at the same surfaces in the state 

* Rodman was to some degree successful in applying the principle 
of initial tension to solid guns, the cast-iron smooth-bore guns known 
by his name having been cast hollow and cooled from the interior with 
the object of securing compression of the bore and tension of the outer 
parts of the finished gun; and the application of essentially the same 
process to steel guns, either cast or forged in one piece, has been shown 
to be feasible and advantageous. 


Elastic Strength of Guns 


201 


of rest; they are always plus, excepting that P () , P„ and P„, being 
only atmospheric pressures, are considered to he zero.* 

T 0 , T x , . .. .T n are the circumferential stresses in the state of 
action, and T 0 , T x ,....T n are the circumferential stresses in 
the state of rest, at the successive surfaces whose radii are R 0 , 
R i? ....R„; they are plus when tensions and minus when com¬ 
pressions. 

e p (R 0 ), e p (R x ), ... .e„(R„) are the radial strains, and e t (R 0 ), 
et(Ri), •.. .et(Rn) are the circumferential strains at radii R 0 , 
R x , • •. . R n , in the state of action; the same symbols with a dash 
over each, as c p (R 0 ), are the corresponding strains in the state 
of rest; they are all plus when lengthenings and minus when 
shortenings. 

Since the states of stress and strain on either side of the surface 
of contact of two elementary cylinders may be different (must be 
if they were assembled with shrinkage), it is necessary to dis¬ 
tinguish between them. A prime mark over any letter or symbol 
indicates that it refers to the outer of the two surfaces which are 
united by the contact. Thus T x is the tension at the inner surface 
of the second cylinder as distinguished from T x which is the 
tension at the outer surface of the first cylinder; e p (R./) is the 
radial strain in the outer of the two surfaces which meet at R 2 ; 
Eet(Ri') and Eet(R x ) are the circumferential true stresses in the 
outer and inner of the two surfaces which meet at R x ; and so on. 
(At R 0 and R n no prime marks are needed, as there is but one 
surface at each.) 

p 0 , p x . p n are the simultaneous changes in the radial pres¬ 

sures P 0 , P x , . .. .P„ resulting from any cause, for example, as 
the cessation of the internal pressure P 0 . 

220 . Evidently, with any given assemblage of elementary cylin¬ 
ders, the elastic strength to resist internal pressure will be greatest 
when in the state of action each cylinder is strained to its elastic 
limit. Moreover, in a compound cylinder so assembled that all the 
elementary cylinders reach their elastic limits of strain simul¬ 
taneously under the action of the internal pressure P 0 , that pres¬ 
sure must be greater than the pressure P, which acts at the surface 

* This convention that radial stresses which are compressive shall be 
called positive, is explained in 190; it must be remembered, however, that 
a radial strain, like all other strains, is called minus when it denotes a 
decrease of length. 



202 


Naval Ordnance 


of contact of the two innermost elementary cylinders; and the 
pressures at the different surfaces of contact must diminish suc¬ 
cessively, P 1 being greater than P.,, P., greater than P.., and so on ; 
for the reason that each of these pressures is balanced by the con¬ 
tractile force of only that part of the compound cylinder which is 
outside of it. 

We will first consider a compound cylinder composed of two 
elementary cylinders so assembled that each reaches the limit of 
its elastic strength when the internal pressure P 0 acts. 

Then, since the outer cylinder is at its elastic limit of strain 
under the sole action of an internal pressure P it we have, applying 
Eq. (20), 


Pi = 


3(Rx-R x 2 ) 
4R 2 2 + 2R 1 * 


*1. 


(29) 


And, since the inner cylinder is at its elastic limit of strain under 
the joint action of an internal pressure P 0 and an external pressure 
P 19 of which pressures P 0 is the greater, we have, applying (27) 
and (28), either 


PM 


_ Ei? 1 J -i?,r)Po + 2PA 1 2 

4 R 2 -2R* 


(30) 


or 


PoW 


3^1! 


-R*)O q + 6 P,R* 
4 R 1 2 + 2R n 2 


(30 


of which (30) gives the value of P 0 which will bring the inner 
surface to its elastic limit of strain by radial compression, while 
(3 1 ) gives the value of P 0 which will bring the inner surface to its 
elastic limit of strain by circumferential extension. The least of 
these two values of P 0 is the true value of the maximum allowable 
internal pressure, but, since which will be tbe least depends upon 
the values of P x , R 0 and R lt we have to express both values, and 
we therefore distinguish between them as shown. 

221. Having ascertained what maximum internal pressure our 
assumed compound cylinder will safely withstand, we have next to 
determine its condition when the internal pressure is removed, for 
no part of it must be overstrained either in the state of action or 
in the state of rest. 

The state of rest differs from the state of action solely in the 
cessation of P 0 ; this must reduce P x , and consequently the outer 
cylinder, which is subjected to no other pressure than P x , must be 





Elastic Strength of Guns 


203 


under less strain after the removal of P 0 than while it acts; the 
inner cylinder, however, while under a less external pressure, is no 
longer supported by P 0 and so may be under greater strain in the 
state of rest than it was in the state of action. To determine 
whether this be so, we must find the value of the external pressure 
to which the inner cylinder is subjected after P () has been removed. 

Putting r = R x in (13), we obtain for the value of the circum¬ 
ferential strain at the outer surface of the inner cylinder ( R„ and 
P„ becoming P, and P i in this case) 


c t (R l ) = 


E 


6 P 0 R 0 2 -P l ( 4 R 0 2 + 2 R, 2 ) 


3 (^i" 


K 2 


(32) 


Also, remembering that the radii of the outer cylinder are R x 
and R>, and that it is subjected only to an internal pressure P x , we 
obtain for the value of the circumferential strain at the inner sur¬ 
face of the outer cylinder 


et(R l ') = 


1 

E 


-p x ( 2 R 2 + 4R.fY 

. 3 (R- 2 2 —R\~) - 


(33) 


These equations, giving the strains caused by the pressures P 0 
and P lf will also give the changes of strain resulting from simul¬ 
taneous changes of the pressures (p 0 and p x ). But the surfaces 
of contact of the elementary cylinders must contract and expand 
together, and so the change of circumferential strain at the outer 
surface of the inner cylinder must equal that which simultaneously 
occurs at the inner surface of the cylinder embracing it. Hence, 
substituting p 0 for P 0 and p x and P x in the second numbers of (32) 
and (33), and equating them, we obtain the following relation 
between simultaneous changes of pressure at r = R 0 and r = R l : 


^PqRo* p\ (4^-0" T 2 R x ■) _ p x ( 2 R x ~ + 4PV) 
SiRY-Ro 2 ) 3(RP-RP) 

3 p 0 R 0 2 (R 2 2 -R 1 2 )=3 PiRi 2 (RS~Ro 2 ), 

R 0 2 (R 2 2 -R t 2 ) 


Pi 


Po- 


(34) 


RYiRP-RY) 

Any change of pressure ( p 0 ) at the inner surface, where r = R 0 , 
will cause the change of pressure (/q) at the surface of contact, 
where r = R x , given by (34) ; and, vice versa, any change p x will 
cause the change p 0 , given by (34). Therefore, putting p 0 = — P 0 
in (34), we have the change in P x which results from the suppres- 











204 


Naval Ordnance 


sion of the internal pressure P 0 , and so P 1 = P 1 — 

R X £ (R 2 * — K n ‘) 

is the external pressure to which the inner cylinder is subjected in 

the state of rest, and this must not exceed „ - p 0 , which has 

been shown in Art. 209 to be the greatest external pressure which, 
acting alone on the cylinder, is allowable. 

222. The shrinkage.—The excesses of the exterior diameters 
of the elementary cylinders, before assemblage, over the interior 
diameters of the cylinders which are to embrace them are called 
the shri>ikages, and are designated by 6\, S 2 , N 3 , etc., being the 
shrinkage of the cylinder whose interior radius is R t , S. 2 that of 
the cylinder whose interior radius is R 2 , etc.* The differences of 

S S S 

diameter per unit of diameter, - ' , —A-, —A-, etc., are called the 

2 /vj 2 i \ 2 2 i \. 3 

relative shrinkages, and are designated by <£ x , <f> 2 , </> 3 , etc. 



Referring to Fig. 37, Oa and Ob represent the inner and outer 
radii of the inner of two elementary cylinders, and Ob' and Oc the 
inner and outer radii of the outer one, before assembling, so that 
2 b'b = S l is the shrinkage; while OA, OP and OC represent the 
inner radius ( R 0 ), the radius of the surface of contact (R x ) and 
the outer radius (R«) after assemblage. When the internal pres¬ 
sure P 0 acts, the compound cylinder is expanded, the three radii 
becoming OA’, OB’ and OC', respectively, and, by hypothesis, in 
this state the inner surface of the outer cylinder is under the cir- 

Q 

cumferential true stress 0 1 ; i. e., its circumferential strain is 

h. 

* The shrinkages are so small in comparison with the radii that it is 
unnecessary to distinguish Ri ± Si from Ri, R 2 ± S 2 from R 2 , etc., in the 
various formulas. 





Elastic Strength of Guns 


205 


But the change of the inner radius of the outer cylinder from its 
free state to the state of action is OB' — Ob '; therefore OB' — Ob' — 
R 6 

—p—- And the change of the outer radius of the inner cylinder 


from its free state to the state of action is OB' —Ob, and this, by 

(3 2 )> is 


Hence 


R.CtiRO 


Rr r6P 0 i? 0 2 -P 1 ( 4 ^o 2 + ^, 2 )l 

E l 3 (tfx 2 -tfo 2 ) J 


S 1 = 2b'b = 2 [ 0 B'-Ob'- (OB'-Ob)} 

is given by 

C _ 2 R x [ a 6P 0 P 0 2 -P 1 ( 4 P 0 2 + 2 P 1 a )l 

1_ £ L 1 3(£x 2 -£o 2 ) J* 


(35) 


223 . The formulas which we have deduced for this case of a 
compound cylinder composed of but two elementary cylinders are 
grouped together in (36). 


(a) 

£x = 

(b) 

Po( 0 ) = 

GO 

Po(p) = 

(c) 

P < = 

(d) 

Si = 


4RS + 2R* 

_3( P 1 2 -Po 2 )0o + 6P 1 P 1 * 

4 P 1 2 + 2P 0 2 


4 R 1 2 - 2 R 0 

p £q 2 (£A-£ 
1 R t 2 (R*-R 

2 R 1 


a 1 Pi( 4 -£o” + zRp) ~6P n P () - 
3 (P 1 2 -P 0 2 ) 


(36) 


To apply these formulas, calculate P x and the two values of P 0 
by (a), (b) and (b'), using for 6 lf 6 0 and p 0 the elastic limits of the 
material as determined in the testing machine; then, with P x and 
the least of the two values of P 0 , determine whether the condition 
required by (c) is fulfilled ; if it is, calculate 5 \ with the same 
values of P x and P 0 ; if it is not, find new values of P t and P 0 , 
using the same values of 0 O and p 0 but a value of 0, sufficiently less 


* Note that the expression in (36c) following the sign < is equation (24) 
in Art. 209 when the definite radius R 1 is substituted for the general 
radius P»; that is, it is the maximum P u Naturally the value of Pi ob¬ 
tained from the expression to the left of the sign must not exceed the 
maximum pressure that a cylinder under external pressure only may stand, 
hence this test. 






















206 


Naval Ordnance 


than the first value assigned it to cause the condition of (c) to be 
met. 

224 . As an example, we will determine the strength of a com¬ 
pound cylinder of steel for which R 0 = 3 in., Ri = 5 ’ n -> ^ = 8 in., 
6 x = 24 tons per sq. in., and 6 0 = p 0 =i8 tons per sq. in. 


P x — 3 ( 64 t 2 5 ) x 24 = 9.18, 

256 + 50 

p ( f )\- 3( 2 5—9) x 18 + 6x25 X9.18 
ol ; 100+18 

p / 3( 2 5—9) X 18 + 2x25x9.18 

°^ p) 100-18 


18.99, 

16.13. 


An internal pressure of 16.13 tons per sq. in. will bring the 
radial strain of the inner surface to the elastic limit, and so this is 
the greatest safe pressure, although the circumferential strain 
does not reach the elastic limit unless the internal pressure is 
raised to 18.99 tons P er sc l- in- We therefore proceed to see if 
the condition of equation (c) is met with the values P 1 = 9-i8, 

^0 = 16.13- 


9.18 — 


9(64-25) 

2 5(64-9) 


X io.i3< ° x 18, 
° 50 


9.18 —4.i2<576, 


5-°6<5-/6. 


The external pressure on the inner cylinder in the state of rest is 
5.06 tons per sq. in., while it is capable of withstanding 5.76 tons 
per sq. in. Therefore the values F^q.iS and F 0 = 16.13 are 
allowable, and we proceed to determine the shrinkage. 



10 

13000 

10 

13000 


24 + 


9.18(36+50) -6x 16.13x9' 


24 — 1.699 


3( 2 5-9) 

.01715. 


9 


The inner diameter of the outer cylinder must be bored to a 
diameter .01715 inches less than the outer diameter of the inner 
cylinder, and, if assembled with this shrinkage, the compound 
cylinder can be safely subjected to the internal pressure 16.13 tons 
per sq. in. 

225 . If the shrinkage used in assembling the compound cylinder 
be known, the resulting strains and elastic strength are determined 
as follows: 












Elastic Strength of Guns 


207 


As shown in 222 and illustrated by Fig. 37, the shrinkage is the 
sum of the contraction of the inner diameter of the outer cylinder 
and the expansion of the outer diameter of the inner cylinder 
which would result from disassembling them. In other words, 
the relative shrinkage is given by </> 1 = e f (/? 1 ') — e t (R 1 ), in which 
et(Ri) and e t {R 1 ) are the circumferential strains at the two 
surfaces of contact which the pressure between them after assem¬ 
blage (in this case P x ) causes. The values of Ct(R x ) and et(R x ) 
we obtain from equation (13). 

First taking the jacket to find et(Ri), we substitute P x for P 0 ; 
R x for R 0 ; R 2 for R n ; R x for r; and P n = o, which gives 


et(R 1 ') = 


L [.£ 

E L 3 

=— r 

E L 3(^2 


3_ (R. 2 _ 

2 P x R , ■ + 4 P 1 R 1 


«r) 3 


X 


■Rp) 


R 2 R 2 P X 
(R 2 2 -R x 2 ) " R x 2 
p 1 ( 2 R l 2 + 4 R-r) l 
E L 3 (R*-R*) J 


Next, taking the tube to find et(R x ), we substitute P x for P„; 
R x for r; and P 0 = o, which gives 


* (*!)=-£- 


p x -R 1 R 1 2 
L 3 x (R x 2 -R 0 2 ) 



-Rq 2 RSPi 

(R x 2 -R 0 2 ) 




2 P,R 2 4 R 2 P x I 

3 ( R x 2 -R 0 2 ) 3 (R x 2 -R 0 2 )1 


but 


1 

~E 


P X ( 2 R X 2 + 4 R 2 ) 

L 3(Ri 2 -R 0 2 ) J 


( p 1 — ct(R 1 ') — et(R x ), 


or 


I 

\P x ( 2 R x 2 + 4 R 2 2 )-] 


I 

/P x ( 2 R x 2 + 4 R 0 2 )\1 

E 

L 3 (rp-Ri 2 ) J 


L E 

\ 3 (Ri 2 -Ro 2 ) /J 


which, after simplifying and clearing, gives 


p F (Rr-R<r)(R/-RE) + 

tl — C' 2 / D 2_ Z? 2\ Vl- 


2 R 2 (R 2 2 -R 2 ) 


(37) 


This equation (37) gives the value of the pressure at the surface 
of contact caused by placing a cylinder of radii R x and R., over a 
cylinder of radii R 0 and R x with the relative shrinkage <f> x . The 
resulting circumferential strain at R 0 , i. e., et(R 0 ), is found from 





























208 


Naval Ordnance 


equation (13) by substituting P 1 for P „; R x for R„; R 0 for r; and 
P 0 = o, which gives 


'«< (K) = -p 


2 v --P,#, 2 + 4 v R^R.H-P,) x J__ 


~ V J 1“1 4- V _ 

3 R 2 -R 0 2 3 RS-K 2 

1 r — 2P x R x 2 , -4 RfP* 1 

R 13 (Ri 2 -_Ro 2 ) 3(RS-R» 2 )1 

2 P,R 2 


R 2 

JV -o 


(R x 2 -R 0 2 )\ 


Now substituting the value of P, from equation (37), we have 


e t (R 0 ) = - -g 


2R 2 


p {R 2 -R 2 ){R 2 -R 2 ) n 
2 R 2 (R 2 -R 2 ) 


{R 2 -R 0 2 ) 

1 r2Fr[£(^ 2 -^o 2 )(^ 2 -^r)^ 


^ / /? \__ _ A L^v AV i AV o A iV 2 ^ v i )' 

o) ~ E L 2 R 1 2 (R 2 2 -R 0 2 )(R 1 2 -R 0 2 ) 


p ( j? — _ R 2 —Ri ,l 
^( R o) R*-R 2 ^’ 


(38) 


by which the relative compression of the bore of the inner cylinder 
caused by superposing the outer cylinder with the relative shrink¬ 
age (f > 1 may be computed. 

Since the only stress at the inner surface in the state of rest is 
the circumferential compression, the radial strain is one-third the 
circumferential strain given by (38). 


Examples. 

(1) Given F 0 =i.8o", R x — 2. 85", R . 2 = 4.50", 6 0 = p 0 — 18.75 tons, 
6 1 =p 1 = 21.50 tons; find P 0 ( 6 ), P 0 (p) and S x ; also the compres¬ 
sion at R 0 in the state of rest. 

P 0 ( 6 ) = 17.11; P 0 (p) = 15.58 tons. 

S x = .0074 in. 

F 1 = 3.6i ; Ee t (R 0 ) = — 12.02 tons. 

(2) Given R 0 = 2. 85", R x = 4.70", R 2 = 7 - 50", 6 0 = Po = 18.75 tons, 
0 i = pi = 21.5 tons; find P 0 ( 6 ), P tt (p) and ; also the compres¬ 
sion at R 0 in the state of rest. 

P ffl (*) = 17.88; P 0 (p) = 15-91 tons. 

^ = .0130 in. 

^i = 4 - 03 ; Ee t (R 0 ) = - 12.75 tons. 





















Elastic Strength of Guns 


2oy 


(3) Given fl 0 = 4 .oo", 6.35”, P 2 = 8.o 4 ", 0 o = Po = i8.5 tons, 

^i = Pi = 2I ° tons; find P 0 (6), P 0 (p) and ; also the compression 
at R 0 in the state of rest. 

P 0 (d) = 12.64; P 0 (p) = 13.26 tons. 

5 \ = .oi26 in. 

P\ — 2.01 ; Ec((R 0 )= — 6.67 tons. 

(4) Given R 0 = 6.00", R x = 8.70", #0=10.46", ( 9 0 =p 0 = 18.5 tons, 
0 \=p 1 = 2\.o tons; find P 0 (6), P 0 (p ) and .S^ ; also the compression 
at R 0 in the state of rest. 

P o (0) = 10.25; P<,(p) = i 1.9 1 tons. 

6' 1 = .oi48 in. 

^i=i- 37 ; Ee t (R 0 )= - 5.22 tons. 

(5) Given #<> = 4.00", ^ = 5.80", #0 = 7.14", 6» 0 = / o 0 =18.5 tons, 
^i = Pi = 2I -° tons; find P 0 (6), P 0 (/a) and ; also the compression 
at # 0 in the state of rest. 

P o ( 0 ) = 10.60; P 0 (p) ” 12.19 tons. 

6' 1 = .oio 5 in. 

Pi= 1-53 ; Eet(R 0 )= - 5.83 tons. 

(6) Given #,, = 4.00", P 1 = 5.8o", #0 = 7.14", if the shrinkage 
was # 1 = .oi05, what is the pressure at the surface of contact and 
what is the compression of the bore (at #„) in the state of rest? 
(Compare result with answers to example (5).) 

^i=i- 53 ; Ee t (R 0 )= - 5.83 tons. 


Section V.—The Elastic Strength of Compound Cylinders.— 

Continued. 

226 . The true stresses, circumferential and radial, at the inner 
and outer surfaces of each of the elementary cylinders are readily 
calculated by (13) and (14), which, when applied to the case of a 
compound cylinder of two parts, become 


Circumferential True Stresses. 

P„(2Rr, + 4#?) —6 P,/?-’ 


Ee t (R u ) = 
Ee,(RO = 


3(R? - RS) 

6P 0 RS-P,( 4 RS + 2R») 
3(R?-R u ) 


Ep (R ,)- PiW,+4RI> 

Ee.lR,) 3 (Rl-Rj) 


Ee, (/? 2 ) = 


2P,R1 
Ri ~ R'i 


(39) 


Radial True Stresses. 


Ee p (R 0 ) = 


2P x R\ + Pq(2RI - 4 P?) 

3(1?? - Ri) 


(40) 


Ee„(.R l ) = 


Ee p (R !) = 
Ee p (R.,) = 


PiUR ii - *Rj) - zPoRi 

3(1?! - Ri) 

P i (2 R*,- 4 RZ) 

3 (Rl ~ P?) 

- 2P1P? 

3 (PI-P?) 


15 


I 












210 


Naval Ordnance 


in which, for the state of action, P 0 and P 1 have the values used in 
calculating the shrinkage, and, for the state of rest, P t) is zero and 
P x is the pressure at the surface of contact when P () = o(P 1 ). 

Applying (39) and (40) to the example worked out in 224 for 
which P 0 = 16.13, P 1 = 9.i 8 and P l = $.o6, we obtain the results 
illustrated in Fig. 38, the right-hand side of which represents cir¬ 
cumferential and the left-hand side radial true stresses, full lines 
indicating the state of action and dotted lines the state of rest. 

It will be seen that in the state of action both cylinders are at 
the elastic limit of strain, the inner one radially and the outer one 
circumferentially. 




Fig. 38. 

Radial True Stresses. Circumferential True Stresses. 

- State of action. -- State of action. 

-“ “ rest. — --“ “ rest. 


227 . The fact that the greater the value of P 0 used in calculating 
the shrinkage the less the shrinkage and consequently the less the 
stresses in the state of rest, suggests an investigation of the results 
of always using P o (0) in (36d) instead of using P 0 (p) when it is 
the smaller of the two values of F 0 . 

In the example of 224 the shrinkage found by using P 0 ( p ) = 
16.13 tons was 0.01715”; if we had used P 0 (6) = 18.99 tons, we 
would have found the shrinkage to be 0.01468”, or nearly 0.0025” 
less. The true stresses in the states of action and of rest have 
been computed for the greater shrinkage; we will now determine 
their values under the same conditions (F 0 = 16.13 tons and 
P 0 = o), supposing the reduced shrinkage to be used. 














Elastic Strength of Guns 


211 


With the reduced shrinkage the value ^ = 9.18 corresponds to 
P 0 18.99* and so we have first to find the change in P x which 
results from reducing P 0 from 18.99 to 16.13; this by (34) is 
— 0.73, making the value of P x for our assumed state of action 
9.18 —0.73 = 8.45. Substituting the values P 0 = 16.13 and P,= 
^•45 ( 39 ) and (40). we obtain the values of the true stresses in 


the state of action. For the state of rest we find P x = 4.33 by 
(36c), getting the same result, of course, whether we use P 0 = 
18.99 and P x =g.i 8 or P 0 = 16.13 and ^ = 8.45; then, putting 

P 0 = o and P x = P x = 4.33 in (39) and (40), we get the values of 
the true stresses in the state of rest. 

The following table gives, side by side, the true stresses result¬ 
ing from the use of the full and the reduced shrinkap-es : 





Circumferential 

Stress. 

Radial Stress. 




Full 

Reduced 

Full 

Reduced 




shrink¬ 

shrink¬ 

shrink¬ 

shrinK- 




age. 

age. 

age. 

age. 

State of Action 
P 0 = 16.13 tons. 

Inner cylinder, inner surface 
“ “ outer “ 

Outer “ inner “ 

+ 10.97 
+ 1.70 
+24.00 

+ 1325 
+ 3.01 
+22.09 

— 18.00 

- 8.73 
—16.t6 

— 18.76 
-8.52 
—14.88 


r Inner 

outer 

+ 11.77 

+ 10.83 

- 3-92 

— 3 - 6 i 

State of Rest. 

“ inner “ 

—iS-81 

- 13-53 

+ 5-27 

+ 4 - 5 t 

Outer 

outer “ 

- 9-07 

- 7-76 

— 1.48 

— 1.26 


“ inner “ 

+ 13-23 

+ 11 33 

— 8.91 

— 7.62 



“ outer “ 

+ 6.49 

+ 5-55 

— 2.16 

- 1.85 


228 . It will be seen that the reduced shrinkage, given by adopt¬ 
ing Po( 6 ) instead of P 0 (p) as the value of P 0 , results in a slight 
loss of elastic strength,* since the internal pressure (16.13 tons), 
which with full shrinkage just compressed the inner surface to its 
elastic limit of strain radially, with the reduced shrinkage com¬ 
presses that surface slightly beyond its elastic limit. As an offset 
to this, the smaller shrinkage considerably reduces all the stresses 
in the state of rest, and those of the outer cylinder in the state of 
action. Moreover, there is reason to suppose that the elastic 
strength to resist radial compression in the case of a cylinder wall 
confined by an outer cylinder is greater than would be indicated 
by the elastic limit of compression of specimens of its material, so 


* With the reduced shrinkage the internal pressure which will bring 
the inner surface to its elastic limit of radial strain is given by 
RS — Ro 2 3 (Rx— Ro 2 ) P o + 2 PiR i 2 


Po = 


R 1 2 — ko 2 


4 R 2 — 2R0 2 


the value of which for the 


example of 224 is 15.62 tons. 








212 


Naval Ordnance 


that the value of P 0 (p ) may probably be exceeded without pro¬ 
ducing any permanent set. At all events, it is not radial com¬ 
pression. but circumferential extension, an excessive value of 
which will cause enlargement and ultimately rupture, and we are 
therefore adopting a measure of safety when we adjust the shrink¬ 
age so as to cause the elementary cylinders to reach their elastic 
limits of circumferential strain simultaneously, even though it be 
under a pressure greater than that which will cause the inner one 
of them to reach its elastic limit of radial strain. 

For these reasons the Ordnance Departments of the United 
States Army and Navy have adopted the practice of disregard¬ 
ing the values of P 0 (p) and determining the shrinkages for the 
superposed cylinders of their built-up steel guns by using the 
values of P„(0). 

We will follow the same method, using P o (0) for computing 
shrinkages, but still regarding P„(p), when it is less than P„(0), 
as the upper limit of safe internal pressure. 

229 . In Art. 221, by equating the simultaneous changes of cir¬ 
cumferential strain of the two surfaces in contact at R x , we found 
the relation (34) between simultaneous changes of P 0 and P x in the 
case of a compound cylinder composed of two elementary cylin¬ 
ders. The same relation might as readily have been found from 
the consideration that, within the elastic limit, the stresses and 
strains resulting from the application of any force are independent 
of prior stresses and strains, so that the effect of an internal pres¬ 
sure is exactly the same upon a compound cylinder as it would be 
upon a simple cylinder of the same dimensions. Thus, putting 
P„ = o and substituting R., for R n in (12), we obtain for the pres¬ 
sure at any point in a homogeneous cylinder of radii R 0 and R., 
under the sole pressure P„ 



and, making r = R x in this, we find 


P(Ri) 


WtMp 

R*(R t *-R 0 *y ot 


which is the same as the relation given by (34). 

230 . The general principle of which the foregoing is an illustra¬ 
tion may be stated as follows: 




Elastic Strength of Guns 


213 


If any pressure be applied to a compound cylinder, the strain 
(or stress ) at each point zvill be the algebraic sum of the strain (or 
stress) at the point before the pressure was applied and the strain 
(or stress) which the same pressure would cause at the corre¬ 
sponding point in a simple cylinder of the same dimensions as the 
compound one. 

231. An important application of this principle shows that the 
maximum strength of any compound cylinder to resist internal 
pressure cannot exceed three-fourths the sum of the elastic limits 
of tension and compression of its inner elementary cylinder, re¬ 
gardless of the strength of its outer parts. For in the state of rest 
the pressure upon the inner cylinder due to the outer ones is limited 
to that which will compress the inner surface circumferentially to 

its elastic limit of compressive strain p jl ; and in the state of action 

the internal pressure is limited to that which will extend the inner 

0 

surface circumferentially to its elastic limit of tensile strain j\ ; 

therefore the greatest allowable value of P 0 is that which, acting 
upon a simple cylinder of the same dimensions as the compound 

one, would cause the circumferential strain Pn at its inner 

h 

surface, and, calling the inner and outer radii R 0 and R n , the value 
of this greatest pressure is by ( 20 ) 


P 0 = 


3 (R,r-R 0 2 ) 

4 R»~ + 2R n ~ 


(Po + 0o)> 


( 42 ) 


the maximum value of which, when R n = 00 , is f(/3 0 + ^o)> or - 
when 0 o =p o , f 6. 

The maximum possible value of the elastic resistance will here¬ 
after be denoted by [P 0 ], and, since we accept the condition 
p 0 = 6 0 , it will be written 


[P 0 ] 


3 (r, 2 -r 2 ) „ 

2 R n 2 + R 0 2 ' 


(43) 


This is the maximum possible value of P u (0) ; P 0 (p) cannot ex¬ 
ceed p 0 in value. 

232. From the formulas for a compound cylinder of two parts, 
those for the general compound cylinder (of n parts) may be 
directly derived, but as the case of three elementary cylinders is 






214 


Naval Ordnance 


the commonest in gun construction, we will deduce the formulas 
for that case separately, and explain how they should be used. 

We begin by finding the values of the pressures in the state of 
action (P 2 , P 1 and P 0 ), supposing the cylinders to have been so 
assembled that they reach their elastic limits of circumferential 
strain simultaneously. 

The outer cylinder being under the sole action of the internal 
pressure P 2 , we have from (20) 


P,{ 0 ) 


3 ( R s 2 - R ^ p 

4 R 3 2 + 2R 2 - 2 ‘ 


(44) 


The middle cylinder being under the external pressure P 2 and 
the internal pressure P 1; of which the latter is the greater, we have 
from (28) 




3(P 2 2 —Pr^+6/y?, 2 

4 R,- + 2R x 2 


( 45 ) 


And the inner cylinder being under the external pressure P t and 
the internal pressure P 0 , of which the latter is the greater, we have 
from (28) 


P o ( 0 ) 


3 (P 1 2 -P 0 2 )fl 0 + 6P 1 P 1 2 

4RS+2RS 


(46) 


Before adopting these values of P 2 , P 1 and P 0 , we must see that 
the shrinkages which they require 'wall not over-compress the inner 
surface in the state of rest. This is most readily done by com¬ 
puting [P 0 ] by (43) and comparing it with P o ( 0 ) from (36b) ; if 
the latter be the greater, the inner surface would be compressed 
beyond its elastic limit of circumferential strain when in the state 
of rest, and so lesser values must be assigned to one or both the 
elastic limits of the outer cylinders and new values of P 2 , P t and 
P 0 computed. When the assumed values of 6 2 , and 6 0 are such 
that [P 0 ] exceeds P o ( 0 ), the inner cylinder will not be too much 
compressed, and then the values of P 2 ( 0 ), P x ( 0 ) and P o ( 0 ) given 
by (42), (43) and (44) may be accepted. 

233 . The formulas for the shrinkages are deduced by the same 
method that was explained in Art. 222. The inner surface of the 
outer cylinder when in the state of action is, by hypothesis, under 


the circumferential strain 


6 2 

E’ 


so that its diameter is 2R0 


E 


greater 


than when it was free (before assembling). If, then, we find the 






Elastic Strength of Guns 


215 


change of diameter ( 2 R 2 e t (R 2 ) ) of the outer surface of the middle 
cylinder which would result from the simultaneous removal of the 
outer cylinder and suppression of the internal pressure P 0 , the 
shrinkage with which the outer cylinder was assembled will evi¬ 
dently be given by S 2 — 2R 2 —£ + 2 R 2 e t (R 2 ). 

By substituting R 2 for R„, P 2 for P n and R 2 for r in (13) we 
obtain the following expression for the circumferential strain at 
the outer surface of a cylinder of radii R 0 and R 2 under internal 
pressure P 0 and external pressure P 2 : 


e t (R 2 ) = 


■ 6 P n R 0 s -Po( 4 R n * + 2 R 2 3 ) 
3 (P 2 2 -P 0 2 ) 


(47) 


But by the principle laid down in Art. 230 the same expression gives 
the change of strain which the application of the same pressures 
will cause in a compound cylinder of the same dimensions. 1 here- 
fore, putting -P 0 and P 0 and -P, for P 2 in (47), we obtain the 
change of circumferential strain at R 2 due to suppressing P 0 and 
P 2 , and this multiplied by 2R 2 will be the change of diameter. 
Consequently the shrinkage of the outer cylinder is given by 


C — 2P; 
E 


0 „ 4- 


P 2 ( 4 Ro 2 + 2 R 9 2 )- 6 P 0 R 0 * 

3 (R 2 2 -R 0 2 ) 


(48) 


Similarly the change of circumferential strain at the outer sur¬ 
face of the inner cylinder due to removing the two outer cylinders 
(i. e., suppressing P x ) and simultaneously suppressing P 0 is 
found to be 




1 

~E 


P 1 ( 4 R 0 2 + 2 R, 2 )- 6 P () R n 2 

. PT^T) ■ 


(49) 


and so the shrinkage of the middle cylinder is 


S, 


_ 2R1 

~ E 


G + 


P l ( 4 R 0 2 + 2 R 1 2 )- 6 P J} Rl 
3(Pr-^o 2 ) 


(50) 


234 . We have, finally, to determine the elastic strength to resist 
internal pressure of the system thus assembled. We know that 
P 0 (</) is the pressure which will bring its elementary cylinders 
simultaneously to their assumed elastic limits of circumferential 
strain, but a less pressure may bring one or more of them to the 
elastic limit of radial strain, and, if so, this latter pressure, and not 
P o ( 0 ), should be taken as the maximum safe pressure. 














216 


Naval Ordnance 


The outer cylinder being under internal pressure only, P-,(6) is 
always less than P-,(p), as explained in Art. 207. Applying (27) 
to the middle and inner cylinders, we obtain the following values 
for the respective internal pressures which will bring them to their 
elastic limits of radial strain: 


p ( \ _ 3(^2 2 ~-^l 2 )Pl+ 2 -^ > 2^2~ 

Ap) 4 R 2 2 -2R 1 2 

p ( \ _ ^0 ~ )pp + 2 P y Rp 

o{p) 4R 1 2 -2R 0 - 


(50 

(52) 


If P^ip) given by (5O ’ s less than the value of P,( 0 ) used in 
computing the shrinkages, then the former is to be used for P A in 
(52) instead of the latter, and if P 0 (p ) given by (52) is less than 
the value of P 0 {6) used in computing the shrinkages, it, and not 
P 0 (6), is the maximum safe pressure. That is, with P 0 (p) </ 3 0 ($), 
the former would be a safe pressure if suitable shrinkages were 
assigned, but since, for good reasons, we adopt shrinkages based 
upon the values of P x (6) and P n ( 0 ), the actual maximum safe 
pressure is somewhat less than P 0 (p). We will call the true maxi¬ 
mum safe pressure P 0 , thus distinguishing it from P 0 (p) and 
P o ( 0 ) ; its value, when it does not equal P 0 (< 9 ), is found as follows: 

The pressures in the state of rest are given by (53) and (54), 
the negative part of each value being the change of pressure due 
to the suppression of P 0 (< 9 ) ■ 


P —p (e) _Ro-(R*--R 2 -) p 

1 2 — 1 2 \ u J R 2 ( R 2 ^ 2j 1 

(53) 

P —P ( 6)— ^"^3 ~ — Rl~) p 

1_ l( j RpiRp-R, 2 ) o( 

(54) 


Then by (14) the radial strain at the inner surface of the inner 

1 2P R 2 

cylinder, in the state of rest, is-^r - - 1 —, and the internal 

pressure which will change this radial strain to — -^! , i. e., which 

h, 

will bring the inner surface to its elastic limit of compression 
radially, is, by the principle of Art. 230, 

p - zW-R, 2 ) ( 2P,R* \ 

0 2R 2 -4R z - 2 V 3(Ri 2 -R 0 2 ) P 7 

p = R^-R q 2 3(Rp-R 0 2 )pq+2P,R 1 2 
0 R 2 -R 2 • ‘ 4R.P-2R 2 


( 55 ) 











Elastic Strength of Guns 


217 


J he same method applied to the middle cylinder, which in the 
state of rest is acted on by P., externally and P, internally, would 
determine the internal pressure which would bring its inner surface 
to the elastic limit of compression radially,* but this pressure will 
practically always be greater than that given by (55), and, accord¬ 
ingly, (55) gives the true elastic strength of the system. 

235 . The formulas for the case of a compound cylinder com¬ 
posed of three elementary cylinders are grouped together in (56) : 


fa'i P — 3 3“ —^2") 
ta) ^ W -' 4 R,‘ + 2 R 7 ~ ’ 

/r\ p ( a\ — +6/TP0 2 

{ } 4RP + 2RS 

(c) p„(fl) = 3 , 

4Ri--t-2R 0 ~ 


(d) P 0 ( 6 )< 


3 ( R/ ~ R »~) (^0+ p«) 


4 R.C T 2R0- 

P (p) _MRp-Rp) P , + 2P 2 R.r 

1Ap) -- 4RP-2R? 

(f) Po(p) = 

(g) 

(h) 


9 

E 


i(r;--rS) p „+2P,r;- 

4R 1 2 -2R 0 - 

2RA a , Po(6) (4R 0 - + 2R. 2 ) —6P n (6)R n 2 ~\ 

”2 1 ' _ / o r~i 1 \ I > 


3 (R-/-Ro 2 ) J 

c _ 2R X f a , P,( 0 )UR n 2 + 2Rr)-6P o (6)R o z -\ 

E L 1+ 3(^i 2 -^o 2 ) J’ 


(0 

(j) 

(k) 


P _P (q\ _ Ro 2 (Rp-Rp) p 

x ~ A } R*(R*-R*} o( ’ 

P _ fr, 3 -flo 2 3(RS-R i ;-) Pn + 2P,RS 
0 R t 2 -R 0 2 ' ~ aRJ-zRJ 


4RS-2RS 


( 56 ) 


The method of procedure is as follows : 

(1) Calculate P 2 ( 0 ), P x { 8 ) and P o ( 0 ) by (a), (b) and (c), 
using for d 2 , 6 X and 6 0 the elastic limits of the materials as deter¬ 
mined in a testing machine. 


* The formula is . 

_ Ri'ats—Ro*) 

* RS(4RZ-2R*)(R* — R*) 


[3 (R? — R, t )p, + 2f\RS — P, 

( 4 P 2 2 -2 P, s )1 . 
























2l8 


Naval Ordnance 


(2) See if the condition (d) is fulfilled. If it is not, find new 
values of P 2 ( 0 ), P x ( 6 ) and P 0 ( 6 ), using values of 6 2 and 6 X (one 
or both) sufficiently less than their true values to cause the con¬ 
dition (d) to be met. 

(3) Calculate the shrinkages by (g) and (h), using the values 
of d 2 , 6 X , P 2 ( 6 ), P x {B) and P () { 6 ) which satisfied (d). 

(4) Calculate P x (p) and P 0 (p) by (e) and (f), using for p 0 
and p x the true elastic limits of the materials, and for P x in (f) 
putting whichever is least, P x (p) or the value of P x { 0 ) calculated 
with the true values of 0 2 and 6 X . 

(5) If P t) (p) is greater than the value of P 0 { 9 ) used in comput¬ 
ing the shrinkages, the latter is the true measure of the elastic 
strength of the system; if it be less, then P 0 , calculated by (k), is 
the true measure. 

236 . To find the state of strain at the inner surface (at R 0 ) 
caused by superposing the two outer cylinders with relative shrink¬ 
ages, respectively and </> 2 , we have only to apply (38) to this 
case, the strain resulting from the compressive action of both 
outer cylinders being merely the sum of the strains caused by 
their actions considered separately. Thus we have 


et(R 0 ) 


RP-R X 2 R. 2 -RP 
RP-R 2 + 1 R*-RP 


( 57 ) 


Moreover, the radial strain at the inner surface in the state of 
rest ( c p (R 0 )) will be one-third the circumferential strain given by 
(57)- 

Examples. 

(1) Given R 0 — y.o", ^=9.5", R 2 = 15.0", R 3 — 2 1.0"; if 9 0 = 
p 0 — 20.0 tons, what is the greatest possible value of the internal 
pressure which can be withstood elastically? If 0 o = 2O.o, ^=21.4 
and 6 2 = 22.t, tons, find P 0 ( 9 ), S x and S 2 . What is the true elastic 
strength after assemblage with the shrinkages based on the value 
of P o { 0 )? 

[^0] =25.26; P 0 ( 6 ) =24.46 tons. 

■S\ = .0183 ; S 2 = .0386. 

P 1 = 4.28 ; P 0 = 18.52 tons. 

(2) Given 7? 0 = 5.0", R x = 9.5", R 2 = 15.0", #3=19.0", 6 0 = P „ = 
20.0 tons; what is the limiting value for the internal pressure? 




Elastic Strength of Guns 


219 


If 0 „ = 20.0, G21 -O, and 6 ., = 24 tons, find P o ( 0 ). If assembled 
with the shrinkages corresponding to the value of P„(0), what 
would be the compression at R 0 in the state of rest ? 

[P 0 ] =26.99; E„(0) =28.39 tons. 

22.06 tons. 

(3) Given # 0 = 6.o", # x = 10.3", #.= 15.0", R z =\y.f, 6> 0 = 17-5 
tons, 0 X = 22.0 tons, 0 ., = 22.o tons; find [P 0 ], P 0 (6), S x and S 2 . 

[P 0 ] =21.97; Po(8) =21.79 tons. 

= .0296; S 2 = .0400 in. 

(4) Given # 0 = 4.75", #1 = 7.50", ^,= 11.375", i^ 3 = I 4 - 375 ". 
^0=16 tons, G =I 7 tons, G = 22.2 tons; find # o (0)> S 1 and S';,. 

# 0 (i 9 ) =20.68 tons; S^.0149; S'., = .0327 in. 

(5) Given # 0 = 6.o", tfi = n.o", # 2 = 17.0", #3 = 21.0", 0 o =i 8 .o, 

G=i9-0, G = 21 tons; find [# 0 ], C* 0 (< 9 ), ^2 and E 0 . 

[-P 0 ] =23.82 ; P 0 (6) =23.82 tons. 

S'! = .0287; #, = .0476 in. 

^ = 6.32; F 0 = 17.23 tons. 

(6) Given # 0 = 6.o", # x =ii.o", #.,= 17.0" and #3 = 21.0", if 
the shrinkages were S'! = .0287 and #, = .0476, find the circum¬ 
ferential and radial true stresses at the inner surface (at R 0 ) in the 
state of rest. Then, by the principle of Art. 230, find the internal 
pressures which will strain the inner surface to the elastic limit 
(18 tons) first radially and second circumferentially. (Compare 
results with answers to example (5).) 

Ee t (R () ) = i8.og; Ee p (R 0 )=6 .03 tons. 

P o ( 0 ) =23.87; # 0 (p) = I 7-25 tons. 

Section VI.—Applications to Built-Up Guns. 

237 . The modern gun is essentially a compound cylinder, but, 
being constructed to withstand an internal pressure which dimin¬ 
ishes from the breech end to the muzzle, the number of layers 
and the exterior dimensions are correspondingly decreased for 
economy of weight, making it necessary to divide the whole length 
into a number of sections for each of which a separate computa¬ 
tion of the elastic strength and shrinkages must be made. In 
United States guns the inner layer, in which are formed the 


220 


Naval Ordnance 


chamber and bore proper, is called the tube; the second layer con¬ 
sists of a jacket, in which the breech block is housed, and chase 
hoops, which extend from the front end of the jacket nearly or 
quite to the muzzle; over that part of the bore in which the maxi¬ 
mum powder pressure acts a third and sometimes a fourth layer of 
hoops is placed. With increase of knowledge and of facilities 
larger and larger steel forgings of assured good quality have 
become available, and the number of separate parts constituting a 
built-up gun has tended to diminish, so that at the present time the 
outer layers, as well as the tube, are sometimes made in one piece. 

In one particular, however, there is an important difference 
between a gun and the compound cylinders with free ends which 
we have thus far considered; in the latter there is no longitudinal 
stress, while in a gun the internal pressure, acting upon the breech 
block as well as upon the cylinder walls, gives gise to a longitudinal 
stress of very considerable intensity. 

238 . The longitudinal stress.—If we consider a gun recoiling 
freely under the action of the powder pressure on the bottom of its 
bore, we see that the total longitudinal stress on any cross-section 
of the gun must equal the product of the acceleration by the mass 
forward of the section,* so that the said stress diminishes rapidly 
as we go forward from the front thread of the screw box, where 
it is a maximum. When recoil is resisted by a brake of any kind, 
the acceleration is reduced and so, to the same extent, is the longi¬ 
tudinal stress on all cross-sections forward of the point of attach¬ 
ment of the brake to the gun ; in rear of that point the longitudinal 
stress is increased by the action of the recoil brake, the increase 
diminishing as the cross-section through the front thread of the 
screw box is approached till, at that point, the total longitudinal 
stress is practically the same as in free recoil. When, as in most 
modern United States naval gun mounts, the pistons of the recoil 
cylinders are attached to a yoke around the breech of the gun, the 
longitudinal stress is diminished at all sections, its maximum value 
M' 

then being (ttR^P — F ), in which M is the whole recoiling 

mass, M' is that part of it which is forward of the front thread of 
the screw box, R 0 is the radius of bore and P the maximum powder 

* F = Ma where F — force ; M = mass, and a = acceleration. 


Elastic Strength of Guns 


221 


pressure, and F is the total resistance * of the recoil brake at the 
instant when P acts. 

We do not know how the total longitudinal stress is distributed 
over the cross-section of the gun. It is not wholly borne by the 
layer in which the breech block houses (the jacket in United States 
guns), for there is an enormous frictional resistance to the longi¬ 
tudinal motion of any one layer relative to the others; if it were 
uniformly distributed over the jacket alone, its intensity, even at 
the section of greatest stress, would seldom exceed 5 or 6 tons 
per square inch, and if, as many writers assume, it is uniformly 
distributed over the whole cross-section of the gun, its greatest 
intensity will not exceed 2 or 3 tons per square inch. Probably 
the latter assumption is practically true at some distance forward 
of the breech block and is not very far from the truth at any point 
forward of the gas check. 

Moreover, this maximum intensity of longitudinal stress only 
exists for the infinitesimally small period of time during which the 
maximum powder pressure is maintained; during the greater part 
of the time in which the gun is subjected to internal pressure the 
longitudinal stress is very small, even at the section where it has its 
greatest value. 

For these reasons, therefore, we are justified in applying to guns 
the formulas which we have deduced for cylinders with free ends. 

239 . If circumferential strain alone had to be considered in tbe 
case of a compound cylinder, the greatest strength would be ob¬ 
tained by making the successive radii of the elementary cylinders 
increase in geometrical progression, provided their physical char¬ 
acteristics were the same. Thus, for the case of any one cylinder 
superimposed upon another, we first substitute the value of P t 
from equation (36a) in equation (36b). Then regarding P 0 (6) 
in (36b) as a function of R x ( R 0 and R 2 constant, and 0 1 = 0 o ), 


and, since we are seeking the maximum value, putting 


dP 0 (6 ) 
dR t 


= 0, 


we find, after simplification, R x 2 = R 0 R. i} which shows that the 
maximum value of P„( 0 ) for a given total thickness of a given 
material occurs when the radius of the common surface is a mean 


* This total resistance of the recoil brake, however, is never more 
than a small fraction of the maximum total pressure on the bottom of 
the bore of the gun. 



222 


Naval Ordnance 


proportional between the inner and outer radii. Very nearly the 
same proportions will also give the greatest strength as regards 
radial strain. 

In practive, however, other considerations govern in the propor¬ 
tioning of the layers of which guns are composed. In the first 
place the layer in which the breech block is housed, even though 
other layers assist it in taking the longitudinal stress, should be of 
sufficient cross-section to itself safely sustain that stress. Again, 
the thickness of the tube over the chamber should be sufficient to 
make relining practicable in case erosion wears away the rifling, 
and its thickness elsewhere should be sufficient to give ample stiff¬ 
ness. Finally, the necessity for keeping down the weight, which 
prescribes a decreasing exterior diameter towards the muzzle, and 
the need for avoiding sudden or great changes of the sections of 
the different layers, often require dimensions not otherwise desir¬ 
able. 

. .. t 

240 . In assigning shrinkages for the different parts of a gun, 
while as a general rule the maximum attainable strength should be 
sought at each section, great changes of shrinkage in passing from 
one section to another must be avoided, as they would cause unde¬ 
sirable inequalities of strain. Not only should each of the parts 
which make up the outer layers of the gun be assembled so that the 
strains at its inner surface, both in the state of rest and in that of 
action, do change abruptly at any point of its length, but the 
tube, similarly throughout its length, should be under a compres¬ 
sion in the state of rest, and of extension in the state of action, 
which only gradually varies and at no point changes abruptly. 
Furthermore, as a rule, slack shrinkages should be preferred to 
excessive ones, to the end that under the action of an excessive 
pressure it may be the tube which gives way rather than an outer 
part. 

241 . As a simple example of the method of determining the 
proper shrinkages, and the elastic strength of a gun, we will con¬ 
sider the case of the United States naval 5-inch B. L. R. Mark V, 
which is shown in Plate I, with its curves of computed elastic 
strength and of strains at rest and in action. 

The computations are made separately for each of the sections 
indicated on the drawing, but only those for the most important 
section, that through the chamber, will be worked out in the text, 
the final results of the other computations, which are obtained in 


Elastic Strength of Guns 


223 


exactly the same way, being merely stated. As it is always neces¬ 
sary to adjust the shrinkages, in accordance with the principle set 
forth in Art. 240, it is most convenient to find their values, as well as 
the values of the pressures in the state of action, in terms of the 
elastic limits of the different layers, afterwards assigning suitable 
values to the elastic limits, always, of course, within their true 
values as indicated by the testing machine. 


ylnch B. L. R. Mark V. 
Section I. 


tfo = 

3-50 

Bo 2 = 

12.25' 

Ri = 

5-25 

Bi 2 = 

27-56 1 

= 

8.25 

R;- = 

68.06 

r 3 = 

10.25 

Ps 2 = 

105.o6 y 


3 (.R 3 *■ 

2 r 3 °- 


I?o 2 )= 278.43-....log 2.44472' 

R 0 2 = 222-37 . “ 2.34707 


00 = Po = 20.0 tons 


60 = 20.0 
Pol = 2 S-4 


0.0976s 
I.30103 

I.39868 


(43) 


01 = Pi = 21.5 

0 2 = p„ = 22.0 

That is, 25.04 tons is the greatest possible elastic strength, whatever the qualities of the 
jacket and hoop. 


3 (R-.r — R< 2 ) = 112.00.log 2.04532 

4 R-S + 2R-S = 556-36. “ 2.74-36 

.... “ 9.29996 

.... “ 1.34242 


A 2 . 

e, = 22.0 


r 


(56a) 


P 2 ( 0 ) = 4-389. “ -64238 

P 2 ( 0 ) = A 2 0 -< = [9.29996] 02 


3(Rr — Ri-y = 121.50.log 2.08458 

4 j? a * + 2R, 2 = 327-36. “ 2.51503 

A .. “ 9-56955 

.. “ 1.33244 


6R 2 - = 408.36....log2.61104 

2.51503 


0 ! = 21 . 5 ... 

7.980. 


.90199 


Bi 

A 2 

BiA~ 


.09601 

9.29996 


9-39597 

1.34242 


•73839 


(56b) 


5-475 ... 

Pi( 0 ) = 13-455 

P,( 0 ) = Ai 0 i + BiA 2 0 3 = [ 9-56955101 + [ 9-39597102 
3(^,2 _ = 43.93. .log 1.66219 6/?!-'= 165.36.-log 2.21843 BiA 2--log 9• 39597 '! 

i 

.08893 


134.74.. 

“ 2.12950 . 

.. “ 2.12950 


“ 9 53260 B 0 . 

.. “ .08893 . 

20.0... 

“ 1.30103 Ai . 

• • “ 9 56955 

6.818 

“ .83363 B 0 A !. 

.. “ 9.65848 BoBiA-2-- 


0, - 21.5... 

.. “ 1-33244 



. . •* .00002 0o = 22.0 



y (56c) 


1-34242 

.82732 


Po( 0 ) = 23-330 

p o (0) = AJ 0 + B 0 A i 0 i + BoBtA-A., = [9-5326o]0 o + [9.6584810! + [9-48490102 

* These are the true elastic limits, being the least values given by 
any of the specimens taken respectively from the tube, jacket and hoop. 




















































224 


Naval Ordnance 


The value of P o ( 0 ) for the true values of the elastic limits being 
23.33 tons, while [P 0 ] =25.04 tons, the inner surface is not too 
much compressed in the state of rest, and so we proceed to deter¬ 


mine the shrinkages. 

6R 0 2 — 73.50.<.log 1.86629 

2/?! = 10.50....log t .02119 

E =13000.0 .... “ 4.11394 

= .0008077- “ 6.90725. “ 6.90725 

4i?0 2 + 2i?! 2 = 104.12.... “ 2.01753 

“ 8.92478 “ 8.77354 

3(Ri 2 — N 0 2 )= 45.93.... “ 1.66210. “ 1.66210 


7.26268....log 7.26268 “ 7.11144...log 7.11144.. .log 7.11144 

Ai ...“ 9-569S5 A„“ 9.53260 t 

BiAn . “ 9-39597 E 0 Aj . “ 9.6584S 

“ 6.83223.... “ 6.65865 BoBtA-i . “ 9.48490 

log 6.64404 “ 6.76992 “ 6.59634 

+ .0008077 6\ + .0006796 0, + .0004557 6-, — .0004406 #„ — .0005887 61 — .0003948 #, 

+ .0006796 — .0003948 

+ .0014873 + .0000609 

—.0005887 


+.0008986 

Nj = .0008986 di — .0004406 do + .0000609 O2 


6R U 2 = 73-50... 





2 R- = 16.50... 

. .log 1.21748 




E = 13000.00... 

., “ 4-11394 




2R: 





■ — .0012692... 
c. 

• ■ “ 7-10354. “ 7-10354 




4R0" + 2/?o 2 — 185.12... 

.. “ 2.26745 





“ 9-37099 “ S.96983 




3<.RA—Ro") = 167-43-•• 

.. “ 2.22383. “ 2.22383 





“ 7.14716. “ 6.74600. 




A, .. 

.. “ 9 • 29996 A 0 “ 9 • 53 2 6o 



• (5^8) 


“ 6..44712 B 0 Ai . 





B 0 B,A 3 . 





“ 6.27860 

“ 6.40448 

“ 6.23090 


+ .0012692#:; 

+ .00028006-2 — .0001899#,, 

— .0002538#! 

— .000170262 


+.0002800 





+.00I549 2 





—.0001702 





+ •0013790 





s ,. 

= .ooi379o#2 — .0001899#,, — 

0002538#! 




Now, substituting the values 20.0, 21.5 and 22.0 for 0„, 0 l and 
respectively, we have for the shrinkages which will cause tube, 
jacket and hoop to simultaneously reach their elastic limits of 
circumferential strain, under the internal pressure P 0 ( 0 ) =23.33 
tons, = .01185 and .So = .02108. 







































Elastic Strength of Guns 


22 


Ro = 

2.70 

Ri = 

5-25 

R,= 

8.25 

R< = 

10.25 

R 0 = 

■* 

2.50 

Rx = 

5-25 

/+ = 

8.25 

R 3 = 

9.00 

- 

R„ = 

2.50' 

A\ = 

5-25 

R.= 

8.00 

R 0 = 

2.50" 


In exactly the same way as shown for Section [. the values of the 
pressures in the state of action and the corresponding shrinkages 
are computed for the other sections, the results being as follows: 

Section II. 

P<(e) = [9.29996] 9. 

Px(o) = [9-56955] 0. + [9.5959 7]0.- 
-Po(0) = [9-69769500 + [9.69170] <9 X + [9.51812502 

51 — 001037601 — .000289600 + .00009830.. 

5 2 = .00 r 397600 — .00015080,, — .000148801 

Section III. 

P 2(0) = [8.92618] 02 
Pi( 6 ) = [9-56955]0i + [ 9.02219 ] 05 
'Po(d) = [9.71671 ]0 O + [9.6989950! 4 - [9.1516350s 

51 — .000947001 — .000246800 + .0000559902 

5 2 = .001250902 — .000191900 — .00018420 

Section IV. 

Pi(0) = [9-54577J01 
-P o (0) = [9.7167G0O+ [9.67521 ]01 
S, = .00093910! — .000246800 

Section V. 

~ . -i 9 ) — [9-46639]0i 
R > = 5-00 J-Po(0) = [9.69897500+ [9-59I33J0, 


Ri — 7.00 J 5’, = .00086930, — .000256400 

Section VI. 

P,(0) = [8.96428] 0i 
• Po(0) — [9.69897500+ [9.08922501 
Si = .00080070, — .000256400 


Ro = 2.50 
R, = 5.00 
R2 = 5-50 


Ro = 

Ri = 


2.50 

5 -oo 


Section VII. 

Po(0) = [9.69897500 


P„= 250] 

^1—38735/ 


R u 
R ■ 


Section VIII. 

[9.55930] 0o 

Section IX. 

)>“ — 4 5 o} /, °^ ) = [ 9 - 65244 ] 0 o 

242 . We adopt as the shrinkages for that part of the gun which 
is represented by Section 1 the values ^ = .0120 and S 2 = .0210, 
being (to the nearest thousandth of an inch) those which result 
from substituting the true values 6 0 , 0 1 and d.. in the expressions 
for S', and S... 

16 


Oi 






226 


Naval Ordnance 


If now we compute the shrinkages for Section II with the same 
values of 6 0 , 6 V and 0. 2 , we find S', = .0165, S., = .oigy and P o (0) = 
27.79 tons, and as the increase of strength over the adjoining sec¬ 
tion would be valueless, while the great increase of the jacket 
shrinkage would cause a very undesirable inequality of strains in 
the state of rest, we see that it will be best to assign less values to 
0 , and 6 ., and to adopt a correspondingly less shrinkage for this 
section. If, on the other hand, we should adopt the same shrink¬ 
ages for Section II as for Section I, an internal pressure which 
would bring the bore to its elastic limit would only cause a cir¬ 
cumferential true stress of about 16.6 tons at the inner surface of 
the jacket, thus causing an undesirable inequality of strains in the 
state of action, since in the adjoining section the jacket reaches its 
elastic limit with the tube. We therefore compromise between the 
two extremes, and adopt the values S'! = .0130 and N 2 = .0200 for 
part of the gun which Section II represents. 

Guided by similar considerations, we assign to the shrinkages at 
the other sections the values stated on the drawing. 

We might now, by means of the general values of and S 2 
which we have computed for each section, find the values of 6 t and 
6 ., which, in combination with the value 20.0 for 6 () , will give the 
shrinkages which have been adopted, and then, with those values 
of 6 0 , G and 0 2 , calculate the elastic strength, compression of bore 
in the state of rest, etc. A better method, however, is to start 
afresh and with the given shrinkages calculate first, by (57), the 
circumferential and radial strains at the surface of the bore in the 
state of rest and then the internal pressure which will increase each 
of those strains to its greatest allowable value. We will do this 
for Section II, as an illustration. 



R 0 = 

2.70 

Ro- 1 

= 7-29 ] 

5 , 



5-, 

.0012381 



R l = 

5.25 

R 1 2 

= 27.56 

— .0130; 0i 

~ 2 R 1 ~ 



R 3 = 

8.25 

R? 

= 68.06 

> 



.S', 




r 3 = 



= 105.06 

A 

— .0200: 0, 


.0012121 



10.25 

R 2 




2/v- 


R\- 

-RS = 

40.5 

. 

.log 1.607 

46 

RS 

— Rr 

= 37-0 

. .log 

1.56820 


(pi = 

.0012381. 

“ 7-OQ2 

75 


0... 

= .0012 

121 .. “ 

7-08354 





0° 

vi 

O 

O 

21 




a 

8.65174 

Rr- 

-R 0 2 = 

60.77 

• 

. “ 1.78369 

R/ 

-ASr 

— 97-77 

ii 

1.99021 



.0008 

251 - 

. “ 6.916 

5 2 








c 

c 

c 

-U 

587. 






ii 

6.66153 


ct ( Ro ) = —.0012838.. 
E = 13000 

Ect (R») — — 16.69 
Ee,( R ») — + 5-56 


7.10850 

411394 

1.22244 





Elastic Strength of Guns 


227 


The true circumferential stress at the surface of the bore in the 
state of rest is thus found to be —16.69 tons, while the true radial 
stress is +5-56 tons. Therefore, applying the principle laid down 
in Art. 230, the internal pressures which will, respectively, bring the 
inner surface to its elastic limits of strain circumferentially and 
radially are found as follows: 


3 (i? 3 2 — Ro 2 ) = 

293-31- • • • 

... .log 2.46733-••• 

-log 2.46733 

60 + 16.69 = 
Po+ 5-56 = 

36.69— 
25.56— 

•••• “ 1.56455 

. ... “ 1.40756 

4AV + 2£o 2 = 
4A/ — 2 Ro- = 

434 - 82 . ... 

405.66- 

“ 4-03188 
- “ 2.63831 

“ 3-87489 

Po(e) = 

24-75 ■ • • • 

• • • • “ 1-39357 


Po(p) = 

18.48.... 




In the same way at each of the other sections the effect upon the 
bore of superposing the outer cylinders with the adopted shrink¬ 
ages is first calculated, and thence the elastic strength of the 
assembled system is determined, the results being as shown by the 
curves in Plate I. 

243 . Since the compression of the bore caused by superposing 

R 2 — R 2 

the hoop with the relative shrinkage </> 2 is by (38) ^ £<£,, 

-^-3 ^-0 

the pressure at the surface of contact in the state of rest must be 



*>*-*•* *.■-*.* £*, 


2 R,- 


R 2 — R 2 

iV 3 1V 0 


(58) 


and, since the whole compression of the bore in the state of rest is 


by (57) R * 


RP-R 0 


Rl -f ^2—^2’ we have similarly 


r 3 2 -r 0 


P i = R£— R o 2 (R 


lr-^0 2 (R£ 
2R 2 \R 2 


Ed, + *»*: 

-R 2 * 1 + R*- 


R.,~ 

Ro 2 


E4 » 2 


(59) 


Thus we obtain the values of the pressures in the state of rest at 
each of the sections of the gun, and from them, together with the 
known value of P 0 , the strains in the state of rest and of action 
may be found. 

















228 


Naval Ordnance 


The following' table gives the results of the calculations for the 
5-inch gun shown in Plate I: 


SECTIONS. 



I' 

1 

11 

III 

IIP 

IV 

V 

VI 

VII 

VIII 

IX 

PoW 

23.89 

23.40 

24-75 

22.71 

20.84 

19.46 

17.69 

12 63 

10.00 

7-25 

8.98 

Po 

18.25 

18.15 

18.48 

VI 

VI 

00 

17.12 

16.64 

16.02 

12.63 

10.00 

7-25 

8 98 

Pi 

2.75 

2.70 

2.66 

1.24 

. 

. 

. 

. 

. 

. 

. 

Pi 

5 - 4 i 

4.83 

6.14 

5-45 

4-54 

3-93 

3-29 

1.28 

. 

. 

. 

Ee,(R 0 ) 

—16.75 

-17-38 

— 16.69 

— 14.09 

— 11.74 

—10.16 

— 8.76 

- 3-41 

. 

. 

. 

Ee t (.R \) 

+ 5-32 

+ 3-92 

+ 7-59 

+ 10.52 

+ 11-65 

+ 11.18 

+ 11.22 

+ 13-88 


.... 

. 

Ee,(R ' 2 ) 

+ 13-79 

+ 13-56 

+ 13-34 

H - 14* 

. 

. 

. 

. 

. 

. 

. 

Ee,(R 0 ) 

+ 11.32 

+ 11.61 

+ 10.71 

+12.60 

+ 14.21 

+ 15-63 

+ 17-28 

+20.00 

+ 20-00 

+20-00 

+20.00 

Ee t (R' 1) 

+ 16.07 

+ 17-69 

+ 15-51 

+ 17-34 

+ 18.40 

+ 17-96 

+ 18.90 

+ 21.38 

. 

. 

. 

Ee,(R' 2 ) 

~h 18.88 

+ 20.09 

+ 17-10 

+ 18.03 

. 

. 

. 

. 

. 

. 

. 


244 . The method of procedure when there are more than three 
layers is exactly the same as has been explained for the cases of 
two and three layers respectively, and the formulas already de¬ 
duced are easily extended to cover any number of layers whatever. 
For the convenience of any one who may wish to use them, the 
formulas for the case of four layers are given in full in an 
appendix. 

Section VII.—Elementary Gun Design.* 

245 . General Considerations.—The modern high-powered gun 
is essentially a compound cylinder designed to withstand rapidly 
varying but not instantaneous internal pressures. The object of 
the subdivision of the gun into various elements is twofold: 1st, 
to increase the range through which the metal of the gun may be 
worked and thus increase the magnitude of the resisting elastic 
forces by assembling the elements with shrinkage; and 2d, to 
insure the homogeneity of the metal and thus the safety of the gun 
by its subdivision into sufficiently small elements. It is a principle 
of metallurgy, in the present state of the art, that there is a prac¬ 
tical limit to the size of cast-steel ingots. If this size, which may 

* Written by Lieutenant (j. g.) R. K. Turner, U. S. Navy, at the Naval 
Gun Factory, February, 1916. 






































CHAPTER VI. PLATE t. 

































































































































Elastic Strength of Guns 


229 


be determined solely by experience for each kind of steel, is ex¬ 
ceeded, the ingot will have unsound areas which no subsequent 
forging can entirely cure. This unsound metal, in the forms com¬ 
monly known as segregations, sand splits, streaks, and blow holes, 
must be carefully avoided during manufacture if the guns are to 
merit a proper degree of confidence. Manufacturing processes 
are undergoing constant improvement, but at the present time two 
principles must be invariably considered in gun construction: 1st, 
that in high-powered guns there should be at least two elements 
resisting stresses whose character is definitely known; and 2d, that 
a sound forging cannot be obtained if its wall thickness, its length, 
and its diameter are all very great. Furthermore, the weight of a 
gun has an important bearing on its mounting on board ship, and 
since the weight increases nearly proportionally to the cube of the 
calibei it is apparent that this fact and the above two considera¬ 
tions tend to limit the caliber and power of naval guns. 

If a pressure curve is drawn from the formulas of interior 
ballistics, it is seen that the whole gun in rear of the base of the 
projectile is subjected to the pressure represented by the successive 
ordinates passed by the projectile during its travel down the bore. 
\\ hen the base is opposite the maximum ordinate the whole gun in 
reai of this ordinate is subjected to the maximum pressure and 
should therefore be cylindrical from the breech to this point. The 
forward portion of the gun, however, is subjected to continuously 
decreasing pressures and may therefore continuously decrease in 
thickness. This decrease in thickness may be theoretically pro¬ 
portional to the decrease in height of the pressure ordinates. For 
this reason the gun is made smaller at the muzzle than at the breech 
and thus an economy in weight and cast is effected. The muzzle 
itself is flared out in the form of a bell because the metal at that 
point is not supported on the forward side and it is thought that 
the absence of slightly extra strength might induce splitting. We 
know that the resistance formulas do not tell the whole truth, 
since they take into consideration neither the supporting nor the 
shearing effect due to the continuation of the metal beyond the 
particular section considered, but experience has shown that the 
formulas in use give the best approximate mathematical measure 
of the strength of the gun as a whole, at least relatively to guns 
of proved worth. 


230 


Naval Ordnance 


246 . Longitudinal resistance.—In the deduction of the resist¬ 
ance formulas the gun is considered to be undergoing strains in the 
planes normal to the axis only. This assumption does not accord 
with the facts, since part of the gun resists for a short time the total 
gas pressure on the face of the breech block. Suppose that section 
of the gun which takes this pressure, i. c., those elements to which 
the block transmits its stresses, have inner and outer radii of R 0 ' 
and Rn, respectively, and the minimum obturator radius is p 0 , the 
bore pressure per square inch being P t) . If the gun did not recoil, 
the section under consideration would, sustain a longitudinal stress 
T in addition to the transverse stresses, such that 


and 


Trp 0 2 P 0 = Tr(Rr ,' 2 — R 0 '-) X T 


T — 

1 D '2 


y P 
1 0 


Rn 2 ~Ro 2 


(75) 


This stress would exist only to the rear of the plane of attachment 
of the gun to the carriage, which is usually a shoulder turned on 
the outside near the breech. A yoke to which the piston rods are 
secured takes against this shoulder. 


As a matter of fact, however, the gun recoils, and in doing so 
relieves this stress to a certain extent. Let W be the weight of the 
recoiling parts, w 1 the weight to the rear of the longitudinal in¬ 
stantaneous center of pressure of the screw-box liner, v the 
velocity of recoil, and R c the constant brake resistance; the total 
effective thrust, F, on the breech of the gun, neglecting the fric¬ 
tion of the projectile in the bore, will be 

r W dv 

r — ma = -j- . 

e dt 


The total rearward force across any section forward of the breech 
diminishes proportionally to the decrease of the mass forward of 
that section. Therefore the maximum stress will be in the plane of 
the longitudinal instantaneous center of pressure between the 
screw-box liner and the gun. The force F' at this point will be: 


77/ / 

r = m a — 


IV — dv 
Z dt 


and the ratio between the two forces is 


F 


F 


W — n\ 

w 


or F’ = F X 


W-vJ 

W * 





Elastic Strength of Guns 


231 


But the total force acting to push the gun to the rear is the differ¬ 
ence between the total gas pressure and the constant brake resist¬ 
ance, or 

F = np , 2 P 0 — Re, 

and therefore the total stress on the metal of the gun is 


and the unit longitudinal stress is 


T = 


F' 


Tr^Rr'-K' 2 ) 


W — W ! v trp 0 2 P 0 Re 

~ W *(Rn' 2 -Ro 2 )‘ 


(76) 


This force acts only in the plane of the instantaneous center of 
longitudinal pressure of the screw-box liner against the threads of 
its housing. From this point forward the stress decreases as far 
as the yoke shoulder. At the yoke shoulder it suddenly changes, 
however, and the only force acting becomes that of the inertia of 
the mass forward of any section considered. If this mass is taken 


equal to , where ur, is the weight of the gun forward of the sec- 
& 

tion considered, the total stress is 




It is useless to attempt to calculate the exact unit stress in any 
layer because the gun is not a homogeneous tube and we cannot 
state the relations between the stresses of the various elements. 
The work is unnecessary, however, because the total force is small 
and may be neglected. 

247 . Gun projects.—The preliminary design of a gun is called 
a project. It includes tentative sketches and rough computations 
as to maximum strength, muzzle velocity, and chamber capacity. 

When it has been decided that a gun of a new type is needed the 
general requirements of such a type are tentatively fixed and the 
project commenced. For instance, suppose that a new gun is 
desired, the progress in artillery having reduced the comparative 
value of the existing type. Progress being usually along lines of 
greater power, reduction of erosion, ease of operation, rapidity of 
fire, or increase in striking energy, it is probable that as many im¬ 
provements as possible along each of these lines will be incor- 






232 


Naval Ordnance 


porated in the new gun. The caliber is first settled upon, and then 
the approximate length in calibers. In the case of small guns the 
muzzle velocity is tentatively fixed, but since erosion is propor¬ 
tionately larger for large guns it usually seems more desirable in 
the case of large calibers to fix the limit of pressure and with that 
pressure to get as high a velocity as possible. Several sets of com¬ 
putations are made with variations of the chamber capacity and 
powder characteristics until a proper combination is secured. 

Suppose it is required to design a 12-inch 50-caliber gun. With 
the three elements of caliber, length, and powder pressure several 
chamber capacities are chosen and calculations made as to the 
effects of several powders in them. From previous experience as 
to the limits of allowable densities of loading the weight of powder 
to be used is approximated and then the various elements varied 
until several reasonable combinations of chamber capacity, weight 
of charge, muzzle velocity, and maximum pressure have been 
obtained. 

For several years the allowable densities of loading have risen 
in value, due to the use of more progressive powders and the 
tendency toward a reduction in the size of chambers for a given 
power. It is desirable to have a short chamber so as to lose as 
little of the travel of the projectile as possible and also to get more 
uniform ignition, and to have a small chambrage in order that the 
outside dimensions of the gun need not be too great. As a general 
rule, though a rule that is departed from without hesitation, it 
may be stated that the length of the chamber is usually between 
6 and 7 calibers, and the chambrage is about 1.20. At least the 
ratio of chamber length to chambrage is kept near these approxi¬ 
mate proportions. 

The general design and method of attachment of the screw-box 
liner are selected. Its length has usually been fixed at about one 
caliber, but the tendency at present seems to be toward an increase 
in this dimension. An attempt is made to eliminate defects that 
may have appeared in previous designs. 

Several drawings are now made of the project. The length in 
all cases is equal to the length in calibers times the caliber plus 
the length of the screw box. 

So many variables enter into a design that experience, based on 
a sound understanding of the principles of gun construction, can be 


Elastic Strength of Guns 


233 


the only safe guide. The consequences of the bursting of a gun in 
service are so grave that all possibility of such an accident must he 
avoided, and yet the gun must not he made excessively heavy nor 
of a form that cannot be mounted in turrets that have proved the 
most satisfactory. Experience has shown the general form a gun 
must take to give the best results with the powders in use at 
present, and no radical changes in this form can be made without 
inviting certain disaster. With any new design it is attempted to 
retain the advantages of previous types and to eliminate any de¬ 
fects that have shown up in service or may seem to be indicated 
by carefully tested theories. Therefore, in laying down a gun the 
previous designs are closely followed so far as regards the general 
outline, thickness and length of elements, mode of attachment of 
the various parts to each other, manner of assembly and approved 
practice in general where it appears to answer the purpose. The 
radical change of too many variables being inadmissible, it follows 
that progress is necessarily slow, and that at one stroke all previous 
defects may not be eliminated and a gun produced that will be 
perfect for all future time. 

With these considerations in mind the outline of the new gun 
will follow closely the outline of a previous gun that seems best 
adapted to the purpose; changes in the outer dimensions will be 
made where it seems necessary and thus the form of the gun will 
be arbitrarily fixed. It may be that a gun of the same caliber will 
not be chosen as a pattern, but one of a smaller or larger caliber 
type that seems to have fulfilled certain of the requirements for the 
new type. 

For two reasons the breech cylinder over the powder chamber is 
usually larger than the slide, which is also cylindrical. The first 
reason is that the chamber diameter under the breech cylinder is 
larger than the bore diameter under the slide cylinder, and there 
must therefore be an increased outside diameter for strength. The 
second reason is that if the gun is heavier at the breech its center of 
gravity will be farther from the muzzle and a smaller length need 
be put inside the turret. The gun usually has an approximately 
constant slope from the slide cylinder to the neck cylinder just in 
rear of the muzzle; the muzzle bell is also a frustrum of a cone 
similar to previous types. 

The question then arises as to the number of layers of metal to 
use. Generally large calibers have either four or five layers: four 


234 


Naval Ordnance 


if the tube is later to be bored for the insertion o.f a liner and five 
if the liner is to be included in the gun as originally built. This 
rule is by no means rigid, however, as witness the 14-inch Mark IV 
gun with four layers, liner included. The practice most in favor 
at the present time is to build five-layer guns with a liner tapered 
from breech to muzzle for easy removal. 

The problem now is to apportion the metal among four layers, 
the inner and outer radii being given. For the greatest theoretical 
transverse strength the law of thickness requires that if R 0 , r, R 
R . 2 and i? 3 are the respective radii from the bore outward, they 
must be connected together by the following relations: 

r* = R 0 R lt R* = R z r, R 2 2 = R 1 R 3 . 

These ratios may not be rigidly adhered to for the following 
reasons: 

1. For large-caliber guns the breech diameter of the liner must 
be great enough to allow for at least three shoulders having a 
height of from o".2 to o'.'25 and the proper taper and yet leave 
sufficient metal at the muzzle for rigidity and for the prevention 
of creep due to the mandrelling effect of the projectile. 

2. It is desirable to have a heavy tube so as to provide rigidity 
for the gun and so prevent droop of the muzzle. 

3. The layer carrying the screw-box liner must have enough 
additional thickness to provide for taking the longitudinal stresses 
without impairing the transverse resistance of the gun. The usual 
rule is to compute this layer for longitudinal strength and then 
make it from 2.5 to 3 times as thick as necessary to carry the longi¬ 
tudinal stress. The extra thickness is taken about equally from the 
contiguous layers on both sides. The calculation for strength is 
usually made by equation (75). 

4. The thickness of the outside layers must not be so great that 
it will be impossible to get good forgings. 

5. Sudden and great changes in the diameter of the gun or its 
component parts must be avoided. 

It is apparent that in the case of a large gun with a large number 
of elements, as, for instance, tbe Mark VII 12-inch 50-caliber gun, 
which is in 12 parts, considerable, juggling will be necessary before 
the above conditions can be satisfied and yet obtain sufficient trans¬ 
verse strength. 


» 

Elastic Strength of Guns 235 

Having decided upon the various diameters near the breech, at 
the forward end of the slide cylinder, and at the neck, the related 
questions of the manner of assembly and the chatacter of the 
joints and shoulders are taken up. The following principles in 
this connection must be rigidly observed : 

1. Joints must be of such a character as to allow the elements to 

be easily assembled. 

2. The tube and liner must be locked to prevent crawl, and all 
other elements must be locked both ways to prevent movement in 
either direction. 

The tube and liner are so long that ordinarily the shrinkage 
friction will prevent rearward motion, but shoulders must be pro¬ 
vided to keep them from going out at the muzzle. 

Locking is accomplished by means of locking rings, locking 
hoops, and shoulders. Locking rings are relatively short and thin 
rings either hooked or screwed to the elements of the gun , they are 
not assembled with shrinkage and do not contribute to the trans¬ 
verse strength. Locking hoops ordinarily attach to the othei ele¬ 
ments by hook joints and are assembled with shrinkage; they are 

longer and heavier than the rings. 

Shoulders are turned on an element to prevent relative longi¬ 
tudinal movement between it and the element shrunk over it. 1 he 
distance between shoulders varies as experience dictates. Their 
height may be from o"2 to i'.'o, the usual height being about o'.'5 
where possible. As a general rule two shoulders are not put in the 
same transverse plane, because a plane of rupture is most likely to 
form at a shoulder, and it is best to scatter the weakest parts so 
that one plane will not include the weak points of several layers. 
The same rule is followed in the case of joints. 

Butt joints are avoided when it is possible to use a lap joint. 
The latter are preferable because they distribute the weakness over 
a greater length, they assist locking and contribute to the stiffness. 
Joints at the outside of the gun in particular must be designed so 
as to prevent droop, as droop is due partly to stretch of the metal 

and partly to working at the joints. 

The several drawings are worked up to embody the various ideas 
that have been expressed. If there are three drawings, for ex¬ 
ample, one may show a heavy gun, one a light gun, and one a gun 
of medium weight, and in each the arrangement will be slightly 


236 


Naval Ordnance 


different. Possibly one drawing will be of a fonr-layer unlined 
gun, one of a four-layer lined gun, and one of a five-layer lined 
gun. Or, in one the joints and layers may be arranged according 
to previous designs and in one they may be laid down on a new 
plan. During their construction the drawings are subjected to 
continuous criticisms and change and new ideas are included as 
they may occur to those in charge of the project. 

Finally, after several weeks’ work, when the various projects 
seem to answer the requirements determined upon, the total weight, 
location of the center of gravity, and an approximate strength 
curve are computed for each. They are then submitted for 
decision and final criticism. 

Usually one of the projects is decided upon, though it may be 
desirable to make a few minor changes in it. The exact chamber 
is definitely selected and, as a rule, the maximum bore pressure and 
the muzzle velocity are fixed, together with the desired weight of 
charge. Orders are then issued for the definite working up of the 
design, and a decision is made as to whether the batteries of one 
or more ships are to be built at once or a type gun only. It is the 
usual practice to build a type gun when a new caliber is in ques¬ 
tion or when the changes have been numerous and radical as com¬ 
pared with existing guns. 

A Mark is then assigned to the design selected. 

As a rule, the drawings are worked up in the following order: 

1. Shrinkages, strength, velocity, and pressure curves. 

2. General arrangement. 

3. Details. 

4. Chamber and breech. 

5. Rough forgings. 

6. Shrinkage sheet. 

7. Center of gravity for shrinkage pit. 

8. Rifling. 

Other drawings may sometimes be required, but these drawings 
are always made, though not always in the above order. 

The breech-mechanism drawings and computations constitute an 
entirely separate set. 


Elastic Strength of Guns 


^37 


Section VIII.—Gun Computations.* 

248 . Preliminary computations.—A pencil drawing of the gun 
is laid down and the sections selected for strength computations. 
These sections vary in number according to the gun ; in some cases 
they are as many as 28. In the case of the gun selected for the 
purposes of illustration, the Mark VI, Modification 3, 12-inch 50- 
caliber gun, computations were made at 24 sections. The sections 
are numbered in Roman numerals, the lowest number being near 
the breech. 

The principle governing the selection of sections may be gen¬ 
erally stated as follows: “ Computations must be made for every 
plane of the gun having a strength different from that of the 
planes on either side of it, and where there is reason to believe a 
sudden change in strength occurs, on both sides of the change and 
close to it.” The plotted results of the computations must give a 
continuous strength curve from breech to muzzle. 

In order to reduce the immense amount of labor involved in the 
case of a gun of large caliber, the computations are made on 
printed forms. The Birnie formulas, involving the introduction 
of subsidiary constants, are used. These are the same as those 
given in this book by Professor Alger, but arranged for greater 
convenience and known as the “Reduced Formulas.” For a 
thorough understanding of their meaning it would be necessary to 
deduce each one from the fundamental equations; this work is not 
given here as it is easy enough, though long. 

In considering these forms we find various methods used that 
are not those that we have been accustomed to. It is important to 
know the formulas on which the forms are based. Logarithms are 
denoted by letters only. An expression such as a s (< 9 :1 ) indicates 
that a 3 is to be multiplied by 0 3 ; therefore their logs are to be 
added. This is further indicated by a + sign after 6 3 . This 
method is used throughout. Expressions are denoted by letters 
or numerals and are thereafter always referred to by such letters 
or numerals. The pressures in the state of rest are denoted by P' 
instead of P as in this text-book. 

Sheets 2, 3 and 4 are used for the preliminary computations and 

Sheet 6 for the final computations. 

* Written by Lieutenant (j. g.) R. K. Turner, U. S. Navy at the Naval 
Gun Factory, February, 1916. 


238 


Naval Ordnance 


It sometimes happens that the dimensions of the gun as laid 
down in the pencil drawing do not give sufficient strength, or that 
a very sudden break in the curve is caused by an improperly de¬ 
signed joint. To correct these faults new dimensions are ten¬ 
tatively assigned or the faults at the joint in question corrected. 
The strength is then computed with the new dimensions. 

249 . Computation forms.—Sheet 1 of the computations is 
headed “ Constants depending on fixed radii and constant modulus 
of elasticity ” and gives the values of the radii and their various 
combinations with each other, together with the logarithms. 

Sheets 2 and 3 are headed “ Computations for reduced formulas 
and maximum values,” and “ Computations for reduced formulas 
and maximum values corrected,” respectively, and give the loga¬ 
rithmic forms for computing: 

1. The maximum elastic forces P m ( 6 m ) and P m (p m ) (for any 
layer m). 

2. A function l m (P m ) of the variations of pressures between the 
state of action and rest. 

3. The pressures, state of rest, P m '. 

4. The initial limiting pressure on the tube, P/. 

5. The adopted values of P O ( 0 O ) and P 0 (p 0 ) corresponding to 
the minimum of P x \ 

6. Pm corresponding to the minimum P/. 

Pm(Om) is the pressure at any surface that will bring the metal 
to its limit of elastic tangential strain at that surface, while P m (pm) 
is the pressure that will bring the metal to the elastic limit of radial 
strain. If the pressure is greater than P m ( 0 m ) the metal will 
actually be permanently stretched tangentially and may even crack 
if the ultimate strength is passed. On the other hand if the pres¬ 
sure is greater than P m (p m ) without being greater than P m { 6 m ) 
the metal will crush slightly and so enlarge the bore, but its tan¬ 
gential tenacity, upon which the actual stability of the gun de¬ 
pends, will in no way be afifected; in other words, P m {p m ) may be 
exceeded without any other efifect than a slight increase in the 
diameter of the bore, so long as the metal at the outside of the 
layer is not strained in the same way beyond its elastic limit. This 
increase in the bore diameter will be very slight and is therefore 
never considered in the case of the inner layer, so that P O ( 0 O ) is 
always used instead of P 0 (p 0 ), no matter which is the smaller. It 
will be otherwise with the other layers, however, because it is 


Elastic Strength of Guns 


239 


apparent that any increase in the bore diameter of any layer 
except the first will reduce the shrinkage of that layer, and will 
therefore decrease the possible range of working of the inner 
layers, thus reducing the elastic tangential resistance. The only 
layer this does not apply to is the outer, since there F„_ 1 (p„_ 1 ) is 
always less than Pn-iX^n-i). Therefore the following rule is 
adopted in computing the successive values of P m ( 6 m ) and 
Pm(pm) '■ “ For computing the successive values of P m ( 0 m ) and 

Pmipm ) always use the smaller of the two quantities, P m+1 
and Pm+i( pm+i') • 

The function l m (p m ) is obtained from the formula 

, (h \_R m 2 ( Rn 2 -R m+ r) 

l m\t m) r> 2 / E> 2 E> 2\ 

-ft-m+i yf'-n -Km, ) 


and ‘is used for the purpose of computing the variations in pres¬ 
sures, p m . The latter is computed with the formula: 

pm+i — pm X lm ( pm ) 

and the pressure, state of rest, from 

Pm —Pm pm • 

The initial limiting pressure on the tube is determined by that 
pressure, P/, which the tube will sustain in the state of rest with¬ 
out passing the elastic limit of compression, since it has been shown 
in the deduction of the formulas (equation 24) that the dangerous 
strain, in a tube subjected to external pressure only, occurs at the 
inner surface and is a tangential compressive strain. If the tube 
is not to be bored for a liner the first of the two formulas, that 
for finding Po ’, is not used, but the second formula only, P( ' being 
taken equal to p 0 and R 0 equal to the inner radius of the tube. 
Both formulas must be used if the tube is to be bored for a liner. 

The “ Pressures, state of rest, relieving jacket ” give first the 
computation of the pressures in the state of action at the inner 
surface of the jacket, using the minimum value of P/, and then the 
pressures in the state of rest in the outer layers of hoops that will 
be required to produce the maximum pressures for the state of 
action when the variations in pressures have been reduced propor¬ 
tionately to the reduction in P 0 . In other words: 

Pm=Pm( max.) -pm- 

This will subject the two outer layers to the maximum elastic 
stress and will reduce the maximum stress in the jacket. Thus all 




240 


Naval Ordnance 


the layers will not participate proportionately in the transverse 
work, and it may happen, when the working limits on Sheet 4 are 
figured, that the metal of the jacket will be found to be strained 
beyond its elastic limit in the state of rest. In this case it will be 
necessary to reassign values of P m ' to the outer hoops to make the 
proper adjustments. Therefore this is essentially a trial method 
and may entail a great deal of additional labor. For this reason 
the set of approximate formulas under “ Pressures, state of rest, 
corrected, relieving hoops ” were adopted and are ordinarily used. 
These formulas relieve the pressures, P m ', on the outer hoops 
proportionately to the reduction in P/ and differ from the theo¬ 
retically correct pressures by negligible amounts, a small constant 
term having been omitted in the derivation of each of the formulas. 
When using this method one may be sure of getting values of P m ' 
that will not over-compress the jacket in the state of rest, though 
the total maximum resistance of the gun may be very slightly 
reduced. The jacket is thus made to do its proper share of the 
work, which is desirable, unless there are special reasons to the 
contrary, as, for instance, when the screw-box liner is attached 
only to a comparatively thin jacket. 

Sheet 4 gives the “ Computations for reduced formulas, shrink¬ 
ages, and compression of the bore,” using the adopted pressures, 
state of rest, corrected, P m '. The formulas are self-explanatory. 

Sheet 5 is a summary of the reduced formulas and a tabulation 
of the values of the subsidiary constants a», b n , c n , etc. This sheet 
is no longer used, however, as it consumes more time than it saves. 
In its place has been substituted Sheet 7, with one set of values 
omitted, viz., the “ Relative shrinkages.” This space is then used 
for writing in the “ adopted ” shrinkages in the adjustment of 
shrinkages. As Sheet 7 gives the absolute values of all the quan¬ 
tities required, instead of their values in terms of the subsidiary 
constants, it is much easier to visualize all the conditions obtaining 
at the various' sections and thus gain a clearer viewpoint for the 
proper adjustment of shrinkages. 

In general the preliminary computations may be considered com¬ 
plete with the completion of Sheets 1, 2, 3 and 4. 

250 . Adjustment of shrinkages.—When the preliminary com¬ 
putations have been finished the values for all sections are tabu¬ 
lated on Sheet 7 as outlined above. It may be noted that the abso¬ 
lute shrinkages come out to six or eight places of decimals, though 


Elastic Strength of Guns 


241 


it is known that it is necessary to allow a plus or minus tolerance 
of about .0005 inch, since large machine turning cannot be clone 
more accurately than that. It is obvious, therefore, that the 
assigned shrinkage can only be given to thousandths of an inch 
and a total tolerance range allowed of .001 inch. 

it will be found that the shrinkages often change their value 
abruptly when computed for maximum strength, and since it is 
not desirable to cut a large number of shoulders on the various 
elements the change must be made gradually in the form of a cone. 
Also, for the sake of economy and accuracy, it is better to have one 
shrinkage extend over the greatest possible length of the surface 
of the element. There are many other practical aspects of the 
subject of shrinkage, as, for instance, the fact that a heavy shrink¬ 
age must not be put on a thin section either for fear of overstrain¬ 
ing the metal or because it is obvious that it will not hold the 
shrinkage until the next envelope is in place. All the various con¬ 
siderations are the result of experience and therefore the assign¬ 
ment of shrinkages can follow no definite rules that will be ap¬ 
plicable to all cases. 

In general, however, shrinkages are assigned the same value 
over as long a surface as possible and the value expressed to the 
nearest thousandth of an inch below the minimum theoretical 
shrinkage for that surface. The various contact surfaces are con¬ 
sidered in order beginning at the inner, and their relation to each 
other must be understood in order to assign proper values. For 
instance, if the theoretical shrinkages are 

6 \ = .ooi6, 5 \> = .0483, .90 = .0571, 
it is at once apparent that must be made greater than .0016, 
because the tube and jacket will not hold together under so small a 
pressure as will result from the use of this shrinkage. Therefore 
a larger value of 5 , is chosen and S 2 and S z decreased so that the 
pressure at the outer surface of the layers in the state of rest will 
not be too great. In this case shrinkages might be assigned as 
follows: 

S { = .012, 5 2 = .040, A 3 = .047. 

A reassignment will be made if these values are shown to be 
unsuitable by the computations on Sheet 6. 

One other general principle of shrinkage is that it is desirable to 
work the tube higher than the outer layers; in other words, the 
tube is to be considered the limping layer. 


1 7 


242 


Naval Ordnance 


251 . Final computations.—The final computations are made on 
Sheet 6 and the results tabulated on Sheet 7, together with the 
maximum theoretical pressures found on Sheets 2, 3 and 4. From 
these tabulated values are constructed the curves of tangential and 
radial resistance and relative compression of the bore. 

Sheet 6 shows the assumed values of the shrinkages and gives 
the forms for the logarithmic computation of values of the com¬ 
pressions, the pressures P m ' and P m , and the tangential compres¬ 
sion resulting from the use of the assigned shrinkages. 

In addition to the formulas for finding the necessary quantities 
are a considerable number of check formulas obtained by the 
transposition of the regular formulas. For instance, there are 
three sets of computations for “ Working limits,” one for check¬ 
ing the theoretical values of P m ( 6 m ) and P m (pm), one for checking 
the assumed values of P m (d m ) and P m (pm), and one for checking 
the values of those quantities after the assumed values of the 
shrinkages have been used. The formulas for “ Working limits” 
give the effective values of 6 m and p m when the various values of 
P m ( 6 m ) and P m (p m ) are used, and in all cases these values must 
be equal to or lower than the respective limits of extension and 
compression for the layer under consideration, except in the case 
of the inner layer, where p t) may exceed the elastic limit. If, for 
instance, the true value of 0 m is 60,000 and we get a value of 
0,,,= 50,000 from the computation of the working limits, the layer 
could be replaced by a layer whose elastic limit of extension is 
50,000 without reducing the height of the strength curve, and 
therefore all the total available strength of the layer will not be 
used when the bore pressure becomes equal to the adopted value of 
P 0 . But if the values of 6 , n or p m are greater than the elastic limits 
either an error has been made or new values of P m must be chosen. 

252 . Computations for the liner.—When a liner is to be 
originally inserted-in the gun it is assembled after the rest of the 
gun has been built up. In this case computations as to its effect 
on the other layers are made, the original computations being 
essentially what would be required for a gun with a bore diameter 
equal to the inner diameter of the tube. 

The formulas are based on the assumption of a two-layer gun, 
the tube, jacket, and hoops forming the outer layer and the liner 
the inner layer. The formulas may be deduced from the theo¬ 
retical formulas for a two-layer giln assembled with the shrinkage 


Elastic Strength of Guns 


243 


assigned for the liner. This shrinkage is small because it is 
desirable to be able to remove the liner and insert a new one with¬ 
out having to bore it out. There is also a possibility of the liner’s 
sticking during assemblage if the shrinkage is very great, since 
the assembled gun must not be heated to too high a temperature 
for fear of disassembly of the elements. 

The computations are arranged on two sheets, Nos. 8 and 9. It 
must be understood that so far as the constants are concerned, the 
liner is treated as a regular layer, R 0 being the bore radius and R t 
the outside radius of the liner. 

Sheet 8 . Assumed Shrinkage—S 

Pressures, state of rest, at R ,.—A pressure P/ on the outside of 
the liner is caused by putting in the liner with a shrinkage S x . 

n , S, _ c w E(RS-R 0 *)(R n 2 -Rp) 

^ 2Ri 2( Rh 2_ Ro Z )xDi • 

Change of pressure in state 'of rest .—These formulas give the 
increase of pressure at the various surfaces that result from the 
insertion of the liner, this causing a pressure of P/ at the inner 
surface of the tube where no pressure existed before. 

pi=Pih, p*=p 2 i* p:=p*%- 

Pressures, state of rest .—The addition of the increase of pres¬ 
sures in the state of rest to the original pressures before the inser¬ 
tion of the liner gives the new pressures, state of rest, at the con¬ 
tact surfaces. 

Pi = pi + Pi (original), 

P i “ pi "T Pi ( original), 

Pi = Pi + Pi (original). 


Tangential compression of bore. — T Po is the tangential compres¬ 
sive stress caused at the inner surface of the liner in the state of 
rest by an outside pressure of P/. 



2RpPi 

Ri-RC 


Strength of gun limited by liner .—The curve drawn through the 
plotted values of P 0 will be the curve of tangential resistance of 
the gun when the stress in the liner has a value of 0 O . 


Po = 


3 (P„ 2 -P 0 2 ) 
4 R,r + 2RC 


(&o + Tpo). 





244 


Naval Ordnance 


Variation of pressitres. —When the gun is fired and a pressure 
P 0 brought into existence in the bore it causes the increase of pres¬ 
sure P m at the other contact surfaces. 


Pl = loPo, P-± — i\P\’ Pz-l-iPl' pi-l-.ip:',' 

Pressures, state of action. — P m is the algebraic sum of the 
pressures, state of rest, and the increase of pressure p,„. The latter 
quantity is considered positive in the present case, since it is one of 
tension with respect to P m ’. 


Pi=Pi+Pi, p*=p; + Pz, P 3 =P*+p 3 , / J 4 =/Y+/V 


Working limits. — 6 m and p m are the stresses in the various layers 
when a pressure P 0 is caused in the bore. 


a - p 3 (o*) 

17 3 — 


0 2 = 

P 2 (0 2 ) 

-A,x 

Pi- 

Pt(p>) 

-P 3 x 

d, 

9 


a. 

a.. 


C., 

e 0 

0i= 


-P,X 

Pi = 

PAp*) 

-P..X 

A 


Oi 

<*t 


Cl 



0o = 

Po(0 0 ) 

-P,X 

Po = 

Pq(Po ) 

-PiX 

d n 

• 

a 0 


C(> 


Co 


When an old gun is to be relined, computations for the liner are 
made in accordance with a somewhat similar set of formulas, the 
chief differences being: 1st, that now r represents the outer radius 
of the liner and R 1 the outer radius of the tube ; and 2d, that 
several additional formulas are necessary to show the changes in 
the pressures, state of rest, at the various contact surfaces that 
will result when the tube is bored and the liner inserted. 

253 . Example of gun computations.—The Mark VII, Modifi¬ 
cation 3, 12-inch 50-caliber gun has been selected for the purposes 
of illustration, the results being given in the case of the section 
over the chamber, number IV. This is an unlined gun, but pro¬ 
vision has been made for the insertion of a conical liner after the 
inner surface of the tube has been worn oiit. 

It will not be necessary to give the formulas used, as they may 
be obtained directly from the computation sheets. The results 
only will be given: 







Elastic Strength of Guns 


245 


In this case: 

7 ? 0 = 15.20 r =17.083 R x - 19.75 R 2 = 26.o 
£3 = 34.0 £ 4 = 44.0 £ = 30,000,00 

6 0 = Po = 55,000 Q x =p r = 60,000 9 2 = 8 3 = p 2 = p 3 = 65,000 

The elastic limits are the specified values, the actual values not 
being used because it would be impossible and undesirable to con¬ 
struct strength curves for each individual gun, one set of curves 
being computed that will apply to all, provided they meet the 
specifications. 

The subscript m will be used to show that a quantity may apply 
to any layer. 

Preliminary Computations. 

SHEET 2 . COMPUTATIONS FOR REDUCED FORMULAS AND MAXIMUM 

VALUES. 

1. Maximum pressures. —Theoretically possible. 

P 3 (0 3 ) = 15.056 

P 3 (0 3 ) =33.21/ P 3 (p 3 ) =39.293 [Use Pi = /*»(«*)] 

P,(0,) = 53,442 Pi(pi) =50.095 [P 2 (P 2 )<P:(p;) Use P* = PM] 

Fo( 0 o) = 70.948 Po(po) = 59,479 lPi(pi)<Pi( 0 i) Use Pi = Pi(pt)] 

2. Working limits. —Check for accuracy of computations for 
( 0 - 

0 3 = 65,ooo 6\ = 60,000 Pl = 60,000 

0 2 =65,000 P , = 65,000 0 O = 55,000 Po = 55,000 

3. Variations of pressures. —Computation of l m (p m ). 

U/>o) = <T-73°°4) IAPi) = ( t - 6 7 2 3 6 ) M./b) = (T-5587 2 ) 

SHEET 3. COMPUTATIONS FOR REDUCED FORMULAS AND MAXIMUM 

VALUES, CORRECTED. 

I 

4. Pressures, siatc of rest. — 1 heoretically possible. 

Pi = 38,105 (F o (0 o )has been used for the reasons given in §79.) 
p 2 = 17,920 £3 = 6,487 

P X ' = P l +(-pl)= 11,990 Pf=Po+ ( -pi) = 15-297 

p 3 '=p 3 +('-£,) = 8.569 

The minimum values of P m are used for the reasons given in §79. 
The quantity p m carries the minus sign because it is negative as 
compared to P m . 


246 


Naval Ordnance 


5. Initial limiting pressure on tube. —This is the value of the 
maximum P/ that will allow the tube to be bored for the liner 
without collapsing. The formulas are based on the assumption of 
a two-layer gun. 

Po= 53.166, P/ = 10,838. 

It will be noted that the Pf given by (4) is greater than that found 
here, therefore the latter value will be used for correcting the 
maximum allowable pressures. 

6. P 0 corresponding to P n -f •—Check for “ Variations of Pres¬ 
sures ” and “ Pressures, State of Rest.” 

P 0 = 70,948. 

7. P 0 corresponding b P,+ ( — Pi)- —Computation of subsidiary 
constants, check for P/, and computation of radial resistance when 
•Co(A) (theoretical) is used. 

C 0 (^0) = 70 , 949 , 

C 0 (po) = 5 2 , 405 - 

It may be noted that the P 0 (p 0 ) found here is less than the theo¬ 
retical C 0 (/3 0 ) ; this will always be the case when P O ( 0 O ) >P 0 (p„) 
as found on Sheet 2. 

8. Pressures corrected. —This gives the maximum theoretical 
P„( 0 O ) and C 0 (/o 0 ) using the minimum of the two values of P/, 
and the maximum variations in pressures corresponding to the 
adopted value of P„. If the initial limiting pressure on the tube is 
not found, this computation is unnecessary. 

P O ( 0 O ) adopted = 67,425 P 0 (p 0 ) adopted = 51.081 

/>, = 36,213 P O ( 0 O ) (adopted) is used for the reason given in §79. 

p2 = 1 7’°3° A = 6-165 

9. Pressures, state of rest, relieving jacket. —See explanation 
of this and the following set of formulas in §249. It may be noted 
that only the first of the three following formulas has been used, 
so as to obtain the pressure, state of action, at the outer surface of 
the tube corresponding to P^min.). The hoops and not the jacket 
have been relieved in this gun. 

C a = 47 , 05 1- 

10. Pressures, state of rest, relieving hoops. —These now be¬ 
come the preliminary adopted values of the pressures in the state 
of rest on the jacket and C-hoop. 

C 2 '= 14 - 537 , P 3 ' = 8,209. 


Elastic Strength of Guns 


247 


SHEET 4. COMPUTATIONS FOR REDUCED FORMULAS, SHRINKAGES, 

AND COMPRESSION OF BORE. 

11. Shrinkages. —The shrinkages here found are those neces¬ 
sary to give the adopted pressures in the state of rest. 

S', = .0092153, S' o = .039499, S 3 = . 050832. 

12. Compressions of bore. —8,, S 2 and 8 3 are the partial relative 
bore compressions that result from the successive shrinkage of the 
three outer layers, and the final relative compression is their sum. 
The same applies to A m , the absolute compressions. 

8, = .00029984 A, = .0045575 

So =.00078837 A, = .011983 

S 3 = .00068397 A 3 = .010260 

S 0 = S,-f So+ S 3 = .00177218 

13. Pf corresponding to 8 0 .—This is a check for (12). 

P/= 10,838. 

14. Tangential compression. 

P = 53,166. 

p should equal the elastic limit of the metal if the theoretical values 
of P,'-has been used. If a lower value has been adopted such that 
the bore of the tube will not be compressed to the elastic limit in the 
state of rest, p will be less than 0 O . 

15. Working limits. —The values of 6 m and p m are the effective 
elastic limits as defined in §251. They are introduced as a check- 
on the accuracy of the preceding work, and to find the relative 
participation of the layers after the outer layers have been relieved 
so that the tube will not be over-compressed when bored for the 
liner. It may be noted that 0 o equals the allowed elastic limit, while 
p 0 greatly exceeds this limit; this is in accordance with what has 
been said in §249. In the case of the other layers neither 6 nor p 
may exceed the proper elastic limits. The ratios of 0 m found here 
to the allowed 6 m show the relative participation of the various 
layers. 

e 0 = 55,000 pQ =78,270 =61,770 p 2 =48,649 

G = 41,842 Pl = 55,77° 0 3 =61,772 

Sheet 5 is no longer used, but Sheet 7 instead. This will be 
called Sheet 7a. 


248 


Nanai. Ordnance 


Final Computations. 

Sheet 7 a is for the adjustment of shrinkages. As the shrinkages 
are adjusted with relation to the other sections, the shrinkages for 
Sections II to IX are tabulated below to show the method used. 

THEORETICAL ABSOLUTE SHRINKAGES. 


age. 

11. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

Si 

<- 

.024954 

.0092313 

.0092153 

.010705 

.010428 

- 4 - 

.013466 

->► 

.01258 

.012470 

.9 2 

t 

-1 

•039574 

.039499 

•039415 

•039428 

■039075 

• 039462 

•037567 

S 3 


•050773 

.050832. 

.050822 

.049281 

.049194 

.049550 

O 

S' 

00 


The small arrows indicate the presence of a shoulder between the 
two sections where they occur. Thus the tube has a shoulder 
between Sections VI and VII. 

From what has been said before it is at once apparent that it 
would be impossible to obtain these theoretical shrinkages on 
account of their wide variations and it would therefore be useless 
and bad practice to assign them. The first thing to do is to ex¬ 
amine this table carefully and then by balancing the various con¬ 
siderations governing the adjustment of shrinkages finally arrive 
at a logical conclusion. 

S x for Section II, where there are two layers only, may at once 
be given a value of .025. 

From Sections III to VI S', varies from .0092313 to .010428. In 
no case may these shrinkages be exceeded Nvithout over-compress¬ 
ing the tube when bored for the liner, so that a proper value of S x 
for these sections seems to be .009. For the same reasons S', from 
Sections VII to IX is given a value of .012. 

Proceeding in this way from one surface to another the shrink¬ 
ages are relieved slightly in every case, until finally the shrinkages 
as given in the table below are tentatively adopted. 





























Elastic Strength oe Guns 


249 


ASSIGNED SHRINKAGES. 


Shrink- 

Section. 

age. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

W 





-> <- 


.025 

.... 

■ .009 


.... 

.012 


.012 


A 








1 

X- 

-> 

«- 




->- 

S2 

• • i 


• 039 

.... 

•037 

.... 

.... 


St 



->- 

<- 




.... 


.050 

.... 

.... 

. 0-17 

... 

.... 


The assigned shrinkages must now satisfy the conditions that 
the tube will not be over-compressed when bored for the liner and 
that no metal in the gun is strained beyond its elastic limit. 
Whether it fulfils these conditions is determined in the computa¬ 
tions on Sheet 6. 

As a matter of fact the shrinkages finally assigned to Section 
III were ^ = .009. W = .025 and S’., = .'025,because the cross-strains 
due to the heavy longitudinal stresses at that section made it 
advisable to relieve the tangential strains that would have occurred 
if the values given in the table had been used. 

When a large change in the assigned shrinkages occurs at a sec¬ 
tion the change is made gradual by the use of a coned surface. 
This method is shown in the small figure in the lower left-hand 
corner of the drawing of the strength curves, etc. 

SHEET 6 . COMPUTATIONS FOR ADJUSTED VALUES. 

These formulas are similar to those on Sheets 2, 3 and 4. except 
that the subsidiary constants do not have to be computed, and the 
correction and most of the check formulas may be omitted. 

16. Assumed values. 

St = .009, So = .039, S 3 = .050. 

17. Shrinkages and compressions. —Computations are made 
using the assumed value of 5 " and subsidiary constants from 
Sheet 4. 

</> t = .00045569 8 t = .00029283 = .0044510 

<t> 2 = .0015000 80= .00077841 a 2 = .011832 

<p.j = . 0014706 83 = .00067279 A., = .010226 

8 U = .00174403 
































250 


Naval Ordnance 


18. Pressures, state of rest. —These are computed from the 
relative compressions and certain subsidiary constants obtained 
from Sheet 4. 

P 3 '= 8,075, P-!— : 4-3 2 ^> Pi- 10,665. 

19. Pf corresponding to S„.—Check for (17) and {18). 

Pf = 10,665. 

The value of Pf must not be greater than the “ Initial limiting 
pressure on tube ” found on Sheet 3. 

20. Tangential compression. —This must not be greater than the 
elastic limit of compression. 

P = 52 , 320 . 

21. Pressures, state of action. —The first five of these formulas 
are similar to those in (8) ; the remainder are those in (4) 
reversed. 

P o (0 0) =66,898 F 0 ( Po ) = 50.883 

^1 = 35.930 Pi- 16,897 p s = 6,117 

^1 = 46,595 P 2 = 31,225 P 3 = 14,192 

22. Working limits. —Relative participation of layers. 

^o — 55’ 000 Po — 77’79^ 

6 ,= 41,610 ^ = 55.286 

6., —61,222 ^2 = 48,164 

d 3 = 60,989 

The values of O m must not be greater than the elastic limit; 6 will 
be equal to the elastic limit of the tube, while in general the values 
of 0 for the other layers will be less than the elastic limits of those 
layers. p 0 may be greater than the elastic limit of the tube, but 
the values of p for the other layers must not be greater than the 
elastic limit. 


SHEET 7 IS THE TABULATION OF THE COMPUTATIONS AND GIVES 

THE VALUES OF 


Formulas 

No. 

. 1. 

U 

<< 

4 - 

a 

u 




D- 

a 

u 

21 . 

a 

a 

18. 


Maximum pressures. 

Initial maximum compression (Pf only). 
Limiting pressure on tube. 

Adjusted pressures. 

a. In action. 

b. At rest. 


Elastic Strength of Guns 


251 


Formulas No. 17. 
“ “ 16. 


a 


u 


a 

a 


1 7 - 
i 7 - 


^2 


20 . 


Shrinkages. 

a. Relative. 

b. Absolute. 
Compressions of bore. 

a. Relative. 

b. Absolute. 

Working limits. 
Tangential compression. 


When all the sections have been computed the curves of tan¬ 
gential resistance, radial resistance, and relative compression of 
the bore are drawn with the values of P o ( 0 o ), P 0 (po)> and 8 0 , 8,, 
8 2 and S 3 computed on Sheet 6. The curves of velocities and pres¬ 
sures in the bore are then drawn for purposes of comparison. It 
will seldom happen that any of the curves will be changed after 
all the sections have been computed, because the strength actually 
obtained for each section is compared with the requirements as 
soon as the computations for the section have been finished. 

Plate II shows the drawings of the “ Shrinkages, strength, 
velocity and pressure curves ” for the Mark VII, Modification 3, 
12-inch 50-caliber gun. 


Section IX.—Formulas for the Case of Compound Cylinders 

of Four Layers. 

254. 


(1) 

/>.(*) = 

(2) 

P,( 0 ) = 

( 3 ) 

PAO) = 

( 4 ) 

P»(. 0 ) = 

( 5 ) 

p,(p) = 

(6) 

PM = 

( 7 ) 

Po(p) = 

(8) 

[P 0 ] = 


Z{R*-R*)6, 

4 R t - + 2R s - 

3(R,--R.:-)e, + 6P,R 3 2 

4R, 2 + 2R.y- 

3(P o 2 -P 1 2 )0 1 + 6/\P, 2 
4R/ + 2RS 

3(P 1 2 -P„ 2 K + 6P 1 P 1 2 
4 Pr + 2P 0 2 ’ 

3 (P rt 2 — R 2 -)pn + 2P :i Rr 

4 l<,r- 2 RP 


3 (RP-R^-) p , 4 - 2 P,R, 2 

4 R*- 2 R* 

3(P 1 2 -P,r) Po + 2P,P 1 2 
4RP-2R 2 

z{R\~ R»~ ) (^o +Po) 

4RS+2R0 2 


(A) 










Naval Ordnance 


If P o ( 0 ) is greater than [P 0 ], the tube will be compressed 
beyond its elastic limit of compression (p 0 ) by shrinkages deter¬ 
mined with the values of P 3 (0), P 2 (0), P, ( 0 ) an d P o (0)> an d so 
the values of one or more of the assumed elastic limits 6 3 , 6 2 and 
( 9 j must be reduced until P o ( 0 ) equals, or is less than, [P 0 ]. 



In these expressions for the shrinkages, the values of 6 Z , 0 2 and 
are not necessarily the real elastic limits, but are the assumed 
elastic limits with which the finally accepted values of P.,(0), 
Pn(6), P,( 0 ) and P o ( 0 ) were calculated. 



(C) 


These are the pressures at the surfaces of contact in the state of 
rest , P 3 (6), P->( 0 ), P t {6) and P o ( 0 ) being the values of the pres¬ 
sures in the state of action used in calculating the assigned 
shrinkages. ' 



(D) 


This is the circumferential strain at the surface of the bore 
caused by the superposition of the three outer layers with their 
respective shrinkages S 2 and S 3 , the successive terms being the 
three circumferential strains produced by the three successive 
layers. 2 R o et(R 0 ) is the change of diameter (contraction) of the 
bore from its free state to that of complete assemblage of the sys¬ 
tem and — Ee t (R 0 ) is the circumferential compression of the bore 
in the state of rest. 

The radial strain at the surface of the bore in the state of rest is 
e p (R 0 ) = — $e t (R 0 ), so that it is under a true tension radially 
one-third as great as its circumferential compression. Therefore 













Elastic Strength of Guns 


253 


the real elastic strength of the system when assembled with shrink¬ 
ages S lf and Sh is the least of the two following values of P 0 : 


(1) pu> = 3 C? 4 _L__ 

4/?4 S + 2^o 8 


( 6 0 -E 5 t (R 0 )), 


(2) IV 2 ’ = Kgl (Po - hEl,(R,,)) 


(E) 


In these expressions it is important to note that dt(R n ) is a 
negative strain, so that the last factor in each of the two values of 
jP„ is numerically the sum, not the difference, of the elastic limits 
(of tension and compression respectively) and the true stresses at 
the surface of the bore in the state of rest (circumferential and 
radial respectively). 

The pressures in the state of rest may be computed directly 
from the shrinkages by the following formulas: 

m 5 - F RS-r/ Rp-R* 2 
{) . R t_ R t • 2 p 3 ’ 

(2) p..=e ~ -:V; + > ( F ) 

(3) 


2RP 

p -p Rp-Ro* 
1 — ^ „ n -1 


-Rn’ 

s.. 

-L 

r;-- 

-rp- 

PA 

-Ro 2 

2 R, 

1 

R 2 - 

-Ro 2 

2 RJ 

-Rp 

■S’, 

■ + 

Rp- 

-Rn' 

Sn 

-Ro 2 

2 R x 

Rz 

-Ro 2 

2 R, 




+ 

R , 2 - 

- Rn- 




Rp- 

-Ro 1 


2 Rp 


The terms in the parentheses are the values of the circumferential 
strains at R n caused by the assemblage of the successive layers, 
their sum with the negative sign being the total compressive strain 
at the surface of the bore as given by equation (D). 

From the pressures in the state of rest, as given by (F), the 
pressures in the state of action may he found by equations (C), 
and the true circumferential tension of the inner surface of any 
layer can then lie found by 

/• n n . _ T> 5\ r, Ti D 2 

(G) 


n < jjf \ Pn ,(4 Rn' + ZRn-t ) —6P„Ru' 

Ee t (R n -i )=— ] - 


3 {RS-RhS) 

In this R n and R„ , are the outer and inner radii of any layer, 
P tl and P„ , are the outer and inner pressures (either of action or 
of rest) and Ee,(R'„ ,) is the true circumferential tension at the 
inner surface of the layer resulting from the action of / » and 1 „ 
Similarly, the true radial compression at the inner surface of 
any layer, either in the state of rest or of action, is given by 

p ,,, v_ /Vi(4 R "!- 2 _R ■ 1 2 ) ~ 2 P i p "i . (H) 















CHAPTER VI. PLATE II. 


3ooc 


2000 



s.«o <rz.5 ».oou 

J 17 (✓COHE 

5.25 -^- 3 ,-fs -| 2 iH S,- 



VooI^^oQl 
. , ,/tconc., i 

f IM 


■Si 




o.oio-oo l 


5,«000^+ OOI 


ELEMENTS OF GUN. 

w«, . f.te Of POWOCR CHAMBER 

I4 6M 

CU IKS 

^^P^TpbojccTile., 

070 

LBS. 

h^r- ( „.- 0F cM*R9t 

336 

LBS 

hrS^ETSF PBOJEc: r 
^frrjrorv- - 

307 62 

2900 

INS. 

r. S. 


SPECIFICATIONS 

PART 

material 

TENSILE 

STRENGTH 

LBS. 

CLASTIC 

LIMIT 

LBS 

ELONG 

% 

CONT 

•A 

TvJBC 

NICKEL STEEL 

90 OO O 

ssooo 

IB 

30 

JACKET 

NICKEL STEEL 

90000 

60000 

IS 

30 

HOOPS 

NICKEL STEEL 

95000 

65000 

1 © 

30 


H 

“ui z: 


u) O.O.P 
r* vf 
N 


S ^ j 


a - vc^ c,1rv CuRv ^ , I.v. 2900 rs, 
b - p«e55u«C CURVE . ErMCROV or ThC PROJCCTILC. 
e - c u* vC ° r m **»**<->m pressure, bxt.iz. 

d - CPU1VAL.CNT PRESSURE. 


ip ,,y..-4Q—^o. 


60 TQ SO 90 100 MO >20 1*0 


r 


0 - 4 +M 4 *L 

ORDNANCE‘ENGINAC*. 

(/ 




gb?r 


SCALE • 


T.3 O H*LLOg*N 

1 gtjj ««t»r 


3 V'J 


SHRINKAGES'. 
STRENGTH .VELOCITY *no 
PRESSURE CURVES. 

SCALE jj, 

U • NAVAL CON fACTONf 
WASHINGTON, O C 
& U~ Z *.'*'3 


7 CTL. . 

•» Dl«CCTI$W«#/»UA€Atl 


UT COMOT .U S **- 


0 13 >3 


euftCAo 

XX 213 iZH#&*&>-. 


NAVY VA AO 


Id 


.17- 


OA AWING <A«0 


45116 




















































































































































































































































































































































































































































































































CHAPTER VII. 


GRAPHIC REPRESENTATION OF THE RELATION 
OF PRESSURES AND SHRINKAGES OF BUILT-UP 
GUNS FOR THE STATES OF ACTION AND REST. 

256 . Object of the diagram.—The object of this diagram is to 
show, graphically, how any one element of the strength of a 
gun, such as shrinkage, pressure in the bore, pressures at contact 
surfaces, in action and at rest, is related to every other element 
and how a modification of one element affects the others. It is 
an attempt to show, graphically, in principle, the coordinate rela¬ 
tion of all conditions of the parts of the gun cylinders between the 
states of action and rest and the limiting conditions for both of 
these states. 

257 . One cylinder.—Strains.—With reference to gun construc¬ 
tion, a simple cylinder under pressure may be overstrained in two 
directions, viz., (i) in the direction of a radius, (2) at light 
angles to the radius or circumferentially. These strains may be 
(1) a radial strain of compression, (2) a radial strain of exten¬ 
sion, (3) a circumferential strain of compression, and (4) a cir¬ 
cumferential strain of extension. 

258 . Pressures.—Radial and circumferential strains may be 
produced, (1) by a pressure P 0 , inside the cylinder, tending to 
burst it, or, (2) by a pressure P n , outside the cylinder, tending to 
collapse it, or, (3) by a combination of these two pressures acting 
at the same moment. 

The equation numbers correspond with those in Chapter VI. 

259 . Internal pressure.—When an internal pressure acts alone, 
the value of the pressure which will just bring the material of 
the cylinder, at its inner surface, to its elastic limit of circumfer¬ 
ential strain is 


PM) 


ZiR.r-R^e 
4R,r + 2R,r ’ 


(20) 


and that pressure which will just bring the inner surface to its 
elastic limit of radial strain is 


P 0 (p) 


3 (R„'- — Rr,-)f> 

'4R7^~2kT 


(22) 


in which 0 and P are the elastic limits of the material of the cylinder 

255 




256 


Naval Ordnance 


under tension and compression, respectively, as determined in a 
testing machine. 

Assume now two axes at right angles, on one of which is 
measured internal pressures, and on the other external pressures. 



Plot on these the values of P„ as determined by equations (20) 
and (22). In this case, as only internal pressure is acting, P„ — o 
and equation (20) will give a value of P o (0) equal, we will assume, 
to Oa, Fig. 40. 

Before plotting the value of P 0 from equation (22) we must 
compare the value of 6 and p. In the case of forged steel used in 
modern gun construction, these elastic limits are usually taken to 
he equal, but with some materials, notably cast iron, p is consider¬ 
ably greater than 6, and even in the case of steel it is probable that 
p is always somewhat greater than 0 . 

Remembering this, a comparison of the denominators of equa¬ 
tions (20) and (22) shows that P n (p) for this case is greater than 
P o ( 0 ) and will plot at b some pressure greater than Oa* 

Recalling now the statement made in the earlier part of the 
text that in gun construction a cylinder must not under any cir¬ 
cumstance be subjected to a pressure which will overstrain it 
circumferentially (see paragraph 228), a glance at Fig. 40 shows 
that as far as the utility of this one simple cylinder, as a gun 
complete in itself, is concerned the interior pressure due to the 
powder must not exceed P o ( 0 ) =Oa, Fig. 40, and that all pressures 
between a and b overstrain the cylinder circumferentially, and are 
therefore unsafe. 


* The only excuse for inserting a diagram of such simplicity in this text 
is to logically lead to the complete graphic representation of all equations. 





Pressures and Shrinkages of Built-Up Guns 


2 5 7 


The outside, or last exterior, cylinder of a built-up gun works 
under identically the same condition as we have here considered, 
and, in gun construction, its strength is determined by that value 
of the interior pressure which will just bring the inner surface to 
its limit of circumferential extension. 


P„ 



260 . External pressure.—Consider now the same simple cylin¬ 
der subjected only to an external pressure P„. 

1 he value of this pressure which will just bring the inner sur¬ 
face of the cylinder to its elastic limit of circumferential strain is 


p ( n\ — (Rn~ R n ~)p 

- JR7- - 


(24) 


and the value of the pressure which will just bring the inner sur¬ 
face of the cylinder to its elastic limit of radial strain is 

p e — _2 P n R„- ( _ 2 Rp \ (or) 

■ 3(Rn 2 -R 0 2 )\ ) ( “ S) 

in which Ec^ — p. This expression will be a maximum when r = R u , 
whence 

2 P n R n 2 


3 (Rn 2 -Ro*) 


(1-2), 


or 


Pn(p)= 3 


( R n R 0 Jp I w ] 1 j c j 1 we w j|] ca ]] (2^) 
2RP J 


Plotting these values on a diagram similar to Fig. 40, we have, 
P u now being zero, Fig. 41. 

18 










258 


Naval Ordnance 


A comparison of (24) and (25a) shows P n (p ) to be three times 
greater than P„(0), but, as it is not admitted, under any circum¬ 
stances in gun construction, that we may allow our cylinders to be 
overstrained circumferentially, tbe strength of the cylinder for 
our purpose is given by the value of P n ( 0 ) = Oc, Fig. 41. 

This is the condition of the tube, or last interior cylinder, of a 
built-up gun in tbe state of rest in which the powder pressure 
ceases to act in the bore. 

261 . Both internal and external pressure acting on a single 
cylinder.—Consider now the case in which both internal and 
external pressures are acting together, and assume the case in 
which the internal pressure is greater than the external. This is 
the case when the powder pressure acts in the bore. 

When P 0 is greater than P n , the case we assume, there are two 
equations expressing the greatest allowable value of P 0 . They 
are 


and 


p (p) — Ro-)p + 2P„R n - 

P»(0) 


4 R n *- 2 R 0 '- 

3(R,:--R { r)6 + 6P„R,r 


4 Rn~ + 2R 0 ~ 


( 27 ) 

(28) 


The first of these gives the value of that pressure inside the bore, 
P 0 , which, acting with P n> will bring the cylinder, at its inner sur¬ 
face, to its elastic limit of strain by radial compression; the second 
gives that value of P n which will bring tbe inner surface to its 
elastic limit of strain circumferentially. The least of these two 
values of P 0 is the true value of the maximum allowable internal 
pressure, but, since which of them will be the least depends upon 
the values of P„, R„, and R 0 , both are expressed. 

For a particular cylinder, i. e., fixed values of 6, p, R n , and R 0 , 
these equations take the form 


P 0 ( p ) =B + CP n (27a) 

and 

P 0 (6)=A+DP n (28a) 


in which A, B, C, and D are constants depending upon the values 
of R 0 , R n , 0, and p. In modern gun construction 0 is usually equal 
to p. 




Pressures and Shrinkages of Built-Up Guns 259 

Equations (27a) and (28a) are equations of two straight lines 
which do not pass through the origin. These may now be plotted 
as shown in Fig. 42. Fig. 42 is the same as Fig. 36, Chapter VI, 
and it is this figure which is the basis of the final graphic solutions. 
The heavy lines given in Fig. 42 are plotted from equations (27a) 
and (28a). That marked P„P 0 ( P ) is plotted from equation (27a), 
and, for any point on this line, its ordinate will give that value of 
P n , and its abscissa that value of P 0 , which, acting together, will 
just bring the inner surface of the cylinder to its elastic limit by 
radial compression. The line P,,P 0 (6) is plotted from equation 
(28a) and its ordinates and abscissie give coincident values of P n 



and P 0 which will just bring the inner surface of the cylinder to 
its elastic limit of strain by circumferential extension. 

This diagram, at a glance, furnishes the following information : 

If the external pressure on the cylinder be a tons per square inch, 
what values may P 0 have? From P n = a, draw a horizontal line 
until it cuts the heavy lines at / and in. There are thus two values 
of P 0 , one P 0 = f tons acting with P n —a tons will bring the inner 
surface of the cylinder to its elastic limit by circumferential exten¬ 
sion. and another P 0 = g tons, which will bring the inner surface 
to its elastic limit of strain by radial compression. 


















26o 


Naval Ordnance 


Similarly, if P n — e tons per square inch, P 0 may have the value 
h, or k, tons. It is to be noted, for this value of P u , that the inner 
surface of the cylinder will reach its elastic limit of radial strain 
before it reaches the elastic limit of strain by circumferential ex¬ 
tension. In other words, for P n — c, the horizontal line through 
P n — e cuts P n P 0 (p) before it cuts the line P„P 0 (6), the reverse 
of what happened at P„ —a. 

When P () = &6 the lines cross, and at this point a value of P„ = c, 
acting with P () = ^0, will bring the inner surface of the cylinder to 
its limits of radial and circumferential strain at the same instant. 

When P n — o, P 0 has two values, A and B, and these values are 
those of equations (20) and (22) as plotted in Fig. 40. 

This figure also shows how the existence of an external pressure 
increases the strength of the gun and allows greater powder pres¬ 
sures to be used in the bore, for when P„ = o, P 0 = either A or B, 
and when P„ = any value greater than o, P t) becomes greater than 
A or B, i. e., it allows a greater value of pressure in the bore before 
the cylinder at its inner surface is strained to its elastic limit 
radially or circumferentially. 

262 . How P„ is developed in gun construction.—Resting 
temporarily from consideration of Fig. 42. consider again the 
simple, single, cylinder as being at rest free from all pressure. 
Suppose there is slipped over the outside of the first cylinder 
another cylinder which just nicely fits the first cylinder while it 
is at rest free from all pressure. Let this second cylinder, the 
jacket, just touch every point at its surface of contact with the 
first cylinder, the tube, without exerting any pressure, both of them 
being in the free normal condition of the metal of which they are 
composed. Now let a pressure, P 0 , be gradually developed inside 
the first cylinder, i. c., inside the tube. 

As this pressure arises the tube will expand, and as it expands 
it will be resisted in its attempt by the restraining influence of the 
jacket and a pressure thus set up at the surface of contact. There 
is thus produced an external pressure on the tube. 

As P 0 increases the tube will tend to further expand, the jacket 
will further resist this expansion and there will he developed a 
further increase in pressure at the surface of contact of the jacket 
and tube. 

Let R 0 , R j, and R» be the radii of the tube and jacket, re¬ 
spectively, 0 and fj the elastic strength of the tube material, and 


[Pressures and Shrinkages of Built-Up Guns 261 


let p x be the pressure at the surface of contact as developed by the 
action of P 0 in the interior of the tube, i. c., in tbe bore. 

I he value of p x is given by the formula 


pl R*(R s *-R 9 3 ) 


x/v 



(34) 



For our compound cylinder of definite radii, the pressure de¬ 
veloped at the surface of contact (whose radius is R x ) is by (34) 
a fixed fraction of the internal pressure which develops it, and 
equation (34) may be plotted as a straight line, as shown in Fig. 43. 













262 


Naval Ordnance 


In Fig. 44 are combined Figs. 42 and 43, to consider the 
strength of the tube as affected by the pressure p x developed at the 
surface of contact of the tube and the jacket. 

Before discussing Fig. 44, a comment must be made upon the 
notation used in Figs. 42 and 43. All lines are designated by the 
quantities by which they are plotted. Thus, p x P 0 , Fig. 43, is 
plotted with values of P 0 as abscissae and coincident values of />, 
as ordinates. It is to be noted, too, that as far as the tube is con¬ 
cerned p x is a particular case of external pressure for the tube. 
P n has been used to designated external pressures in general on 
the tube. 

Consider now the line p x P 0 in Fig. 44. When the pressure in 
the bore has reached a value P 0 = Ob , the line p x P 0 merely shows 
that the external pressure, p x , at the contact surface, due to the 
restraining influence of the jacket, has reached a value p x = ba. 
But, at a the line p x P 0 cuts the line P n P 0 {6). This last line is that 
for any point of which its coordinates represent a combination of 
internal and external pressure which will just bring the inner 
surface of the tube to its elastic limit of circumferential strain, 
so, the coordinates of the point in which the line p x P 0 cuts P n P o { 0 ) 
will give that value of P 0 beyond which we cannot increase P () 
without overstraining the inner surface of the tube circumferen¬ 
tially, for which value of P 0 = Ob, we have P n = p 1 = ba. 

Similarly, where p x P 0 cuts P n P 0 {p ) in / will give a value of 
P 0 = Od beyond which P 0 may not be increased without overstrain¬ 
ing the tube radially. 

As we cannot allow our cylinder as a gun tube to exceed the 
elastic limit of circumferential strain the strength of our com¬ 
pound cylinder gun, as limited by the tube, if everything else is 
favorable, is given by the value of P 0 = Ob. 

The next question is this: Are other conditions favorable and 
can we adopt this value of P, x = Ob and, basing our powder charges 
on it, have the gun safe? 

Further consideration of pressure developed at the surface of 
contact.—Limits imposed by the jacket.—We cannot answer 
the preceding question without further considering the pressure 
at the surface of contact. This pressure while an external one for 
the tube is an internal one for the jacket. The pressure on the 
exterior of the jacket is the atmosphere and is considered as zero. 


Pressures and Shrinkages of Built-Up Guns 263 


We have, therefore, to consider the effect of p x as an internal pres¬ 
sure on the jacket. 

As p x increases it may reach a value which will overstrain the 
jacket circumferentially before the bore is overstrained, in which 
case we may not exceed in the bore a value of P 0 which will just 
bring the inner surface of the jacket to its elastic limit of circum¬ 
ferential strain. 



Fig. 45. 


That value of p x which will just bring the inner surface of the 
jacket to its elastic limit of circumferential strain, which we desig¬ 
nate by p x (max.) is, see equation (20), 


, , 3(R 0 2 -R x -)6 1 

/q (max.) — aR 2 + 2R 2 


(20) 


in which R 2 and R x are the radii of the jacket and 6 X the elastic 
strength under tension of the material of which the jacket is made. 

As this is the limiting value of the interior pressure of the 
jacket at the surface of contact, it is also the practical limit, for 
the gun, of the external pressure on the tube at the surface of 

contact and we can plot it on Fig. 44. 

As it was desired to have Fig. 44 free from all lines not essen¬ 
tial to the text up to that point, Fig. 44 is reproduced, as lug. 45, 



















2 64 


Naval Ordnance 


with a change essential to consistency in notation. The P„ of the 
original simple cylinder was a general symbol expressing an ex¬ 
ternal pressure on the tube. We have used p x to designate the 
external pressure arising from placing the jacket on the tube and 
as this is so far the only external pressure considered as acting 
the symbol p x is substituted for P„, as shown in Fig. 45. 

Fig. 45 gives the following information : If the strength of the 
jacket limits the value of p x (max.) to Oz, then P 0 cannot exceed 
a value P 0 = om without overstraining the jacket, since by the 
line p x P 0 when P 0 = om, p x — um — Oz and any further increase of 
P 0 will make p x >Oz, although the tube will not, at its inner sur¬ 
face, be overstrained circumferentially until P 0 = Ob, or radially 
until P 0 = od, as determined by tbe intersection of p x P„ with 
PiPo(p) and p x P o (0). 

Again, if p x (max.) as limited by the material of the jacket 
must not exceed Oy, then P t , may have a value On without over¬ 
straining the jacket. But, by referring to tbe intersection of p x P 0 
with p x P 0 {6) at a we see that P 0 must not be allowed to exceed 
P 0 = Ob or the tube will be subjected to a pressure greater than 
that which will overstrain the bore circumferentially. We thus 
see there is for the condition we have just discussed a margin of 
safety in the jacket, as it will allow us to strain the tube to its 
elastic limit circumferentially by a value of P 0 = Ob without being 
brought to its own limit of strain. 

Again, we cannot carry P n to the value Od, which would bring 
the tube to its limit of radial strain, for in so doing p x would rise 
from a to f, and would cause p x — fd — oc^>Oy, therefore Oy is the 
limit of p x allowed by the jacket and must not be exceeded. 

Again, if the jacket permits a value of p x (max.)= 0 .r to be 
safely withstood by itself there would be required, by running 
from x to tbe line />,P 0 and down to o a value of P it = Oo tons 
to develop this value of />,. A glance at the diagram, Fig. 45, will 
show that the combination of P n — Oo and />, = 0 .r is much in 
excess of the conditions represented at a and /. at which points 
the tube is at its limit of circumferential and radial strains. In 
consequence, the extra strength of the jacket which enables it to 
stand an internal pressure p , (max.) —Ox is useless since the tube 
is not strong enough to stand a value of P 0 which will produce 
/q(max.) — ox. 


Pressures and Shrinkages of Built-Up Guns 265 

263 . Two cylinders assembled with shrinkage.—Let us return 
now to the consideration of our original simple cylinder, taking 
it up at the point at which we were about to slip the jacket on it. 
Assume, also, that the jacket was too small to slip over the tube, 
and that we are compelled to heat it, causing it to expand suffici¬ 
ently to allow it to be slipped over the tube, and that from this con¬ 
dition, while in place on the tube, it is allowed to cool. 

As it cools it will attempt to contract, or shrink, and return to 
its original diameter. This effort to shrink will be resisted by the 
tube and a pressure will be set up at the surface of contact, which 
will increase with the further tendency of the jacket to cool, until 
the jacket and the tube have reached the normal temperature of 
the air. I his pressure will then become stationary. We will 
designate it by P x . 



264 . Effect of pressure due to shrinkage plus pressure de¬ 
veloped at contact surface by the pressure in the bore.—When 
this compound cylinder has cooled and is in equilibrium, the only 
pressure in existence is P x and it is necessary to investigate the 
effect of this, when additional pressure />, at the contact surface, 
due to P 0 in the bore, is brought into existence. 

When P 0 acts, the pressure now at the contact surface is P x + p x . 
The sum of P x + p x we shall denote by P x , it being the resultant 
pressure at the contact surface, due to shrinking on the jacket, and 
to the existence of a pressure in the bore. 






266 


Naval Ordnance 


In Fig. 46 plat the line p x P 0 , which shows the values of the 
pressure at the contact surface due to P 0 , and on the same axes 
draw a line representing P x as produced by the amount of shrink¬ 
age (Nj) with which the cylinders have been assembled. 

Now when P 0 has reached a value Oa, Fig. 46, p x has the value 
ab, and the total pressure at the surface of contact, P x , is 
(Pi + p x ) — ac + ab = ad = P x . 

It is evident that we may obtain instantly the value of P x for 
any value of P 0 by simply drawing through x a line^parallel to 
the line p x P 0 and, that this line, for any given value of P,, will give 
coincident values of the total pressure at the surface of contact 
and pressures in the bore. 

This diagram has another property, as follows: If the point 
d, Fig. 46, represents a condition due to certain coincident values 
of P x and P 0 , and a line be drawn through d parallel to the line 
p x P 0 , the point at which that line cuts the vertical axis 0 P t will 
give ox, which is that value of P x which we must have in order to 
produce the coincident values of P x and P 0 represented by d. 

For example, if the coordinates of d, Fig. 46, were the values 

of P x and P 0 which would just bring the inner surface of the 

tube to its elastic limit of circumferential strain, and we draw a 

^ — 

line through d parallel to p x P 0 we can find what value of P x will 
be necessary in order to have the inner surface of the tube reach 
its elastic limit of circumferential strain under a pressure of 
P n = Oa tons in the bore. 

This knowledge is important because it will enable us directly 
and graphically to show what influence the amount of shrinkage 
has, and what amount is necessary to produce the desired value 
of Pj. 

265 . Shrinkage and P x .—By shrinkage, is meant the difference, 
at the surfaces of contact, of the diameters of the jacket and tube 
before they are assembled. 

The pressure P x produced, at the surface of contact, by shrink¬ 
ing on the jacket is. 

p = E{R*-R*){R Z *-R *) 

1 2R 1 \RJ~R 0 2 ) ~ A 2R x 

in whichis substituted for <f> x (see paragraph 222). 


( 37 ) 




Pressures and Shrinkages of Built-Up Guns 267 

For definite values of R.,, R x , and R n the equation may be plotted 
as a straight line P X S X and combined with Fig. 46, as shown in 
Fig- 47 - 

This diagram gives the following information: What shrink¬ 
age is necessary to produce at the surface of contact a pressure 
P 1 = On tons, when P 0 = Od tons, and what is the pressure due 
to this shrinkage when the gun is in a state of rest, i. c., when the 
powder pressure has disappeared from the bore? 



Solution. —At u, for P 1 = Ou draw ua. At d, for P 0 = Od, erect 
a perpendicular cutting ua in the point a. Through a, draw a line 
parallel to p x P 0 to Then P 1 — Oz. Continuing from z, parallel 
to the horizontal axis to the line P 1 S 1 and then drop to c. Oc is 
the shrinkage desired, and Oz is its corresponding pressure in the 
state of rest. 

If for any reason we wish to maintain P 0 at its value Od tons 
but, because of the jacket cannot allow P 1 to exceed the value bd 
tons, what must be the value of P x and what shrinkage (J^) must 
be used to accomplish this ? 

Solution. —From b draw a line parallel to piPo> cutting the 
vertical axis at x. Then P x = Ox and its corresponding shrinkage 
is S x — Oy. ___ 














268 


Naval Ordnance 


With a given shrinkage Oc and a maximum allowable value of 
P x — On, what is the maximum allowable value of P 0 J . 

Solution .—From c, for S t = Oc, go to PyS and then over to z. 
Through z, draw a line parallel to pyP 0 until it cuts the horizontal 
line through u(P 1 = Ou ) at the point a; drop to d. The maximum 
allowable value of P () is then P () = Od. 


What is the effect on the pressure at rest (Py) if in assigning 
a shrinkage we adopt N^Oy instead of S t = Oc ? 

Solution .—From c and y, run up to PySy and over to z and x. 
P 1 will be reduced from Oz to Ox tons. 


In the preceding case, if Py is to be kept constant at P 1 = Ou, 
how must the pressure in the bore be varied since the shrinkage 
has been reduced? 

Solution .—Through u draw Py — Ou. Through x (the value 
of P v corresponding to the reduced value of the shrinkage) draw 
a line parallel to pyP 0 until it cuts P 1 = Ou in the point r. From 
r drop to t. Therefore, with the reduced shrinkage P 0 must be 
increased from Od to Ot tons if Py is to remain constant, i. e., if 
the jacket is to be worked to its limit. 


If the final pressure at rest, i. e., the pressure Py, due to the 
shrinkage, be too great the tube may collapse through the effect 
of P y acting alone after the powder pressure, P 0 , has left the bore 
and no longer supports the tube. 

Now take the following conditions for a problem: (1) P Q 
must not exceed Od tons or the tube will be overstrained circum¬ 
ferentially while the powder pressure acts. (2) The pressure in 
action at the surface of contact, Py, must not exceed the value 
Py — Ou or the jacket will be overstrained circumferentially dur¬ 
ing the existence of the powder pressure in the bore. (3) The 
value of Py must not exceed Ox or the tube will collapse when the 
powder pressure ceases to act and support the bore. 

Under these conditions, what shrinkage may be used, and will 
the jacket be overstrained, or not, when the tube is just brought 
to its elastic limit of circumferential strain? 





Pressures and Shrinkages of Built-Up Guns 269 


Solution. —At P 0 — Od erect a perpendicular and through x draw 
a line parallel to p x P 0 intersecting the perpendicular from d in the 
point b. Draw bu . Then P 1 = Ow'<P 1 = 0 « and the jacket is not 
overstrained. The shrinkage corresponding to P x — Ox is = Oy. 


Assume the following conditions for a problem: (1) The 

jacket will be brought to its limit of circumferential strain by a 
pressure P 1 = Ou. (2) The tube will be brought to its limit of 
circumferential strain by a pressure P^ — Ot. (3) The tube at 
rest, i. e., when not supported by a powdei^pressure in the bore, 
cannot safely stand a pressure greater than P 1 = Os. 

Problem. —Under these conditions, find what shrinkage must 
be used to bring the tube and jacket simultaneously to their elastic 
limits of circumferential strain, what final pressure at rest will be 
produced, and whether or not the tube can stand this pressure 
when the gun is at rest. 

Solution .—Draw P^Oit and P 0 = Ot intersecting in r. 
Through r draw rx parallel to p x P 0 . The tube will be safe at 
rest because Ox<Oz. The shrinkage corresponding to P ± -Ox 
is 5 ^ = Oy. 


266 . Formulas for a gun of two cylinders.— The formulas 
which follow are those for a gun consisting of a compound cylin¬ 
der composed of two elementary cylinders assembled with 
shrinkage: 


(a) 

(b) 


P 1 (max.) 




4RS + 2RS ’ 


3(Rr-R n 2 )^ + 6P,R/ 

4^ 1 2 + 2i?o 2 


(c) 

(d) 

(e) 


. Po(p) = 


P t (i nax.) = 
/>! = 


3(tfr-# 0 2 )p„+2/VV 

4RS-2RS 

(Rp-R 0 a ) Po 

2 R* 

R ( ?(R.p-Rp)P n 
' RSiRS-Ro*) ’ 


(0 


* 


4RS(R**-R* i )Pi 

*'-E(RS-R,r)iR.r- Rp) 


■ (36) 


* Derived from formula (37) Elastic Strength of Guns. 











270 


Naval Ordnance 


P x (max.) = That pressure at the surface of contact which, if ex¬ 
ceeded, will overstrain the jacket circumferentially. 

F x =The sum of all pressures at the surface of contact 
during the existence of a pressure P 0 in the bore, 
i. c., while the gun is at the instant of firing. It 
is the sum of P x and p x . 

/> 1 =That portion of the total pressure at the surface of 
contact which is developed at that surface by the 
existence of P 0 in the bore. 

P x — The pressure at the contact surface produced by 
shrinking on the jacket. When the gun is not in 
the act of firing P 0 =O, and P x is the only pressure, 
an external one to the tube. If great enough it will 
overstrain the tube and tend to collapse it when P n 
ceases to act. 

P x (max.) = That value of P x which cannot be exceeded without 
overstraining the inner surface of the tube when P 0 
ceases to act. 

S x = The shrinkage producing P x . 

P 0 = Any pressure in the bore. It may be P 0 (6 ) or P 0 (p) 
in value. 

P o (0) = That pressure in the bore which combined with P x at 
the surface of contact will just bring the inner sur¬ 
face of the tube to its elastic limit of circumferential 
strain. 

P 0 (p) = That pressure in the bore which combined with P x at 
the surface of contact will just bring the inner sur¬ 
face of the tube to its elastic limit of radial strain. 

6 0 = p 0 = Elastic strength of material of tube for extension and 
compression. 

8 x = p, = Same for the jacket. 

267. Computed diagram for two cylinders.—A complete dia¬ 
gram for a case of two cylinders is given in Fig. 48. 

The data for this is taken from Art. 224: 

P 0 = 3", Ri = 5”> ^2 = 8", 0 o = Po =i8 tons per sq. in., O x = Px = 2 4 
tons per sq. in. 


Pressures and Shrinkages of Built-Up Guns 271 


For use in plotting Fig. 48, the equations (36) become: 

Pi (max.) =9.18 tons, 

P»(6) = 7 - 3 l + 1 - 2 7 2 P t » 

P 0 (p) = 10.53 + 0.609^, 

P x ( max.) = 5.76, 

h = o- 2554 P 0 , 

P 1 = 2955 1 . 

268 . Discussion of Fig. 48 .—Use of P 0 ($) and P 0 (p)- —From 
the formula P x (max.) the jacket cannot stand a greater pressure 
at the surface of contact than P 1 (max.) =9.18 tons, with which 
value of P 1 a pressure P () = 16.13 tons will bring the tube to its 
elastic limit of radial strain, i. e., P 0 (p) = 16. 13 tons; and, a pres¬ 
sure of P 0 = 18.99 tons will bring the inner surface of the tube to 
its elastic limit of circumferential strain, i. e., P o ( 0 ) = 18.99. 

When Pj(max.) =9.18 and P 0 (p)_= 16.13, P i will have the 
value 5.06 tons which is less than P x ( max.) =5.76. Ihe tube, 
therefore, will be safe at rest and the shrinkage which will just 
bring the jacket to its elastic limit of circumferential strain at the 
same time the tube reaches its elastic limit of radial strain, will 
be (for P x = 5.06) .01715". 

If with this shrinkage we increase P 0 from 16.13 to 18.99, P\ 
will rise above the value 9.18, to c, Fig. 48, and the jacket will be 
overstrained. 

What shrinkage, now, will enable the jacket and the tube to be 
brought simultaneously to their elastic limits of circumferential 
strain? From d(P 1 = P 1 (max 1 ) =9.18, P o = P o ( 0 ) = 18.99) draw 
a line parallel to p x P«. This gives P x = 4-33 and S x = .01468. _ The 
shrinkage is reduced and the pressure in the state of rest, P,, is 
also reduced from 5.06 to 4.33 tons. 

As it is desirable to have as small pressures at rest as is con¬ 
sistent with developing the greatest possible strength of the gun, 
let us see what will be the effect of regulating the shrinkages by 
using P 0 (6) and using P 0 (p) for the limit beyond which we may 

not carry the pressure in the bore. 

Refer to Fig. 48. Starting now from P x — 4.33 ( 5 ' 1 = .01468" 
corresponding to P o ( 0 ) = 18.99) the line of P x rises to 6 = 8.45 tons 
when P 0 (p) = !6-i3 tons. According to our diagram this line cuts 
the P,P 0 (p) line at a, and if we proceed to b will slightly overstrain 


2/2 


Naval Ordnance 


the tube’s inner surface by radial compression if with P x — 4-33 
we carry the pressure in the bore to the value of 16.13 tons. 

It is usually considered that this may be done with safety since 
the value of p 0 used in the formula is the value given by a free 
test of the specimen and not from a test of a specimen supported 
as by a jacket. 

The practice in the Army and Navy is, when F o (0) >F 0 (p) 
calculate shrinkages with it but limit powder pressures by P 0 (p). 
If P 0 d<P 0 (p), then P{6) must be used to determine both shrink¬ 
age and powder pressure. (See Art. 228.) 

Referring again to Fig. 48, and considering it without reference 
to the immediately preceding remarks, we see that our tube in the 
state of rest will stand a maximum pressure from shrinkage of 
Fornax.) =5.76 tons. 

What will be the effect of adopting this shrinkage? The dia¬ 
gram shows that if we start with P x — 5.76 its maximum allowable 
value, Fj will reach its limiting value of 9.18 tons when F 0 = 13.25 
tons. In other words, by adopting this shrinkage the jacket will 
be overstrained long before the tube, and the full strength of the 
compound cylinders cannot be utilized in firing, while the tube in 
the state of rest will be subjected to the maximum pressure due to. 
shrinkage that it can stand without being overstrained. 

The diagram thus shows at a glance the effect of adopting any 
shrinkage intermediate to those commented upon in this text, or 
the effect of the variation of any element for the state of action 
or rest, and the limiting value of the element considered for these 
states. The diagram is easily applied to the case of three 
cylinders. 

269 . The diagram for three cylinders.—Before explaining the 
construction of the diagram for the case of three cylinders it is 
necessary to discuss the effect of superimposing the third cylinder 
upon the two already assembled. 

In the state of rest our compound cylinder composed of two 
simple cylinders assembled with shrinkage is subjected to but one 
pressure P x existing at the surface of contact due to the shrinkage 
Si see (Fig. 49). 

In the state of action there exists F 0 in the bore, its resultant />, 
at the contact surface in addition to F, already existing at that 
surface (see Fig. 50). 


TUBF 


Pressures and Shrinkages of Built-Up Guns 


273 



TO 


SHRINKAGE IN .001" PRESSURES IN BORE IN TONS PER SQ.IN. 

Fig. 48. 



















274 


Naval Ordnance 


Now take the compound cylinder in the state represented by 
Fig. 49 and shrink on it a third cylinder, termed a hoop, with a 
shrinkage of S. : inches. 

The surface at which this third cylinder clasps the jacket is 
called the second contact surface and the pressure at this surface 





Fig. 51. 




Fig. 52. 


due to the shrinkage S 2 with which it is assembled we will desig¬ 
nate by P 2 . P., is in every respect similar to P x as discussed in the 
case of two cylinders, and is governed by the same laws. 

In future, a quantity referring to pressures or shrinkages at the 
second contact surface are denoted by the subscript and those 
for the first contact surface by the subscript x . 








Pressures and Shrinkages of Built-Up Guns 


2/5 


When P., is brought into existence by shrinking the hoop on 
the already assembled jacket and tube, a pressure due to P is 
transmitted through the jacket from the second to the first contact 
surface. This fraction of P», designated by p x , will exist at the 
first contact surface in addition and coincident with the pressure, 
P,, already there due to shrinking the jacket on the tube. 

The three cylinders assembled with shrinkage will, in the state 
of rest, be subjected to pressures as indicated in Fig. 51. 

Starting with the conditions of Fig. 51, let a powder pressure 
P tt be developed in the bore. P 0 produces at the first contact sur¬ 
face a pressure we will designate by p x and p x produces at the 
second contact surface a pressure p.. y both p x and p., existing at 
their respective contact surfaces in addition to the pressures 
already there due to the shrinkages. 

The complete set of pressures for the three cylinders in the 
state of action is indicated in Fig. 52. 

270 . Notation of formulas for three cylinders.— 

E . 


K, R„ I<:, 

6„, $ x> 0., . , 


and 


P.. 

P 


Pi- Pj • 
P P- 

y 1 \y 1 2 


, . Modulus of elasticity. 

, . Radii of surfaces of cylinders. 

, . Elastic limits of metal of tube, hoop, 

jacket under tension. 

, . Elastic limits of same under compression. 

. . Total pressures; in the bore P 0 ; at the first 

contact surface, P x ; and at the second 
contact surface, P.,, with the system in 
action. Their maximum values which can 
be supported without exceeding the elastic 
limits, to be designated by tbe suffix (6) 
or (p) accordingly as they represent pres¬ 
sures producing circumferential or radial 
strains. 

P lt P., .Pressures, P x at first contact surface due to 

shrinking jacket on tube; and, P 2 at sec¬ 
ond contact surface due to shrinking hoop 
on jacket. 

. . Pressure at first contact surface due to P.. 

at second contact surface. 

Sum of all pressures, for the state of rest, 
at the first contact surface. 

lP\ = P 1 + p 1 . 


Px 





Naval Ordnance 


276 


p 1 .With the system in action, p x is the pressure 

at first contact surface due to P 0 in bore. 

p., .With the system in action, p 2 is the pressure 

at second contact surface due to p x at the 
first contact surface. 

S lt S 2 .... Shrinkages, in inches, producing P x and P 2 . 


P 1 (max.), P 2 ( max.) Values of P x and P 2 which cannot be ex¬ 
ceeded without overstraining the jacket 
(P j max.), or hoop (Pjiiax.), hence the 
limiting values of P, and P 2 for the state 
of action. 

2 P 1 (max.) . . . That value of SPj which cannot be exceeded 

without overstraining the tube by com¬ 
pression of the bore when the tube is not 
supported by powder pressure, hence the 
limiting value of for the state of 

rest.* 


* 2P, in this chapter is that designated by Pi in Chapter VI. The symbol 
2Pi is used here because it is desired to indicate that the total pressure at 
the first contact surface is composed of two elements due to separate 
shrinkages. 




Pressures and Shrinkages of Built-Up Guns 277 


* FORMULAS FOR THREE CYLINDERS ASSEMBLED 
WITH SHRINKAGE. 


1 

I. 

II. 

III. 

IV. 

V. 

Part 

affected. 

Character 

of 

pressure. 

Formula. 

Plots 
the line. 

Relationship shown by the line of 
col. IV. 

Hoop. 

Internal. 

P - 3(^3' Rf) 0 i 

PA6) - 4 R.- + 2R/ 

(a) 

°;(max) 

Value above which P 2 cannot 
rise without overstraining the 
hoop circumferentially. 

Jacket. 

External. 

P 3 


General symbol for pressure ex¬ 
ternal to jacket. 

- E (Ro~ — Ro~) (R-c — Ro 2 ) c , 

4 R^(R<r — Ro-) ' 

(b) 

P2S2 

Shows the pressure produced at 
second contact surface by as¬ 
sembling the hoop with any 
shrinkage Ss. 

Ri~ (Rj~ — R?-) 

Ps ~ RSlRf— AV) ' pl 

(c) 


Shows the pressure produced at 
the second contact surface (in 
addition to that already exist¬ 
ing there due to shrinking on 
hoop), by any pressure pi act¬ 
ing at the interior surface of 
the jacket. The line pipi is 
identical in character for the 
jacket with the line p\P 0 for 
the tube. See Figs. 43, 44*and 
46 and discussion thereupon, 
all of which applies in prin¬ 
ciple to the line piPi. 

Internal. 

n 4.4 3 (R ?'— Ri) 0 i+ 6R 2 2 P 2 
4R/ + 2RS 

( d) 

P2P Ad) 

The coordinates of any point on 
this line show what coincident 
values of an external pressure 
P2 with an internal pressure 
Pi will just bring the inner 
surface of the jacket to its 
elastic limit of circumferen¬ 
tial strain. 

0 4 4 3 (R ? 2 — R l 2 )p l +2R./P, 

PM ~ 4 Ks-iRc 

(0 

PSAp) 

Similar to the above for the 
elastic limit of radial strain, 


* Taken principally from Chapter VI, but also from Notes on the Construction of 
Ordnance Nos. 35 and 59, by Major Birnie', U. S. A. The gun is considered as a 
compound cylinder with free ends. 


























































278 


Naval Ordnance 


FORMULAS FOR THREE CYLINDERS ASSEMBLED 
WITH SHRINKAGE.—Continued. 


I. 

II. 

III. 

IV. 

v. 

Part 

affected. 

Character 

of 

pressure. 

Formula. 

Plots 
the line. 

Relationship shown by the line of 
col. IV. 

Jacket. 

Cont’d. 

Internal, 

Cont’d. 

5 E (/?,*— R n ~) (Ry — Rr) S, 

4^1 w —AO 

(/) 

PxSx 

Shows the pressure produced at 
the first contact surface by 
assembling the jacket with 
any shrinkage Su This pres¬ 
sure Pi (in these notes) does 
not include that pressure at 
first contact surface pro¬ 
duced by shrinking on the 
hoop. P 1 refers to the jacket 
alone and exists simultan¬ 
eously with but distinct from 
px- 

_ R^(R^-R^) - 

pl Rr(R/ —Ro s ) 2 

(g) 

hP, 

Indicates what fraction of P 2 is 
included, at first contact sur¬ 
face, in the value of 2 Pi. It 
gives the element of pressure 
at the first contact surface 
due to P : at the second sur¬ 
face. It is used to graphically 
separate 2A, into />, and P u 

„ Ro 2 (R> s -Rx 2 ) n 
h AY (AY—AT) n 

ih) 

| 

’"0 

c 

Shows the pressure produced at 
the first contact surface by P 3 
in the bore. This pressure. 
pi, is in addition to any pres¬ 
sure due to shrinkages al¬ 
ready existing at the first 
contact surface. See Figs. 
4 . 3 » 44 and 46 and discussion 
thereto. 

Tube. 

External. 

1 \ 

(1) 


General symbol for total pres¬ 
sure at first contact surface 
for the state of action. It is 
therefore the sum of /’i+pj-f- 
P 1 at any instant. 

Px 

O') 

PxSx 

Same as (/) for jacket. It is an 
internal pressure for the 
jacket but external to tube. 















































Pressures and Shrinkages of Built-Up Guns 279 


FORMULAS FOR THREE CYLINDERS ASSEMBLED 
WITH SHRINKAGE.—Continued. 


I. 

II. 

III. 

IV. 

V. 

Part 

affected. 

Character 

of 

pressure. 

Formula, 

Plots 
the line. 

Relationship shown by the line of 
col. IV. 

Tube 

Cont’d. 

External, 

Cont’d. 

^P 1 = P 1 + p t 

( k ) 

.... 

Sum of all pressures at first 
contact surface in the state 
of rest. 

^75 , , (R^—Ro 2 ) 

lri(max= ,, • p 0 

2 Ri 

(!) 

.... 

Maximum value of the pres¬ 
sures, due to collective 
shrinkages, which the tube 
can stand and not be over¬ 
compressed when the powder 
pressure does not support the 
bore. 

/>! 

(m) 

pxPo 

Same as (h) for the jacket. It 
is internal for jacket, ex¬ 
ternal to bore. 

Pa 

<«) 

.... 

General symbol for pressure in 
the bore, may have Po( 0 ) or 
P 0 (P) as a particular value. 

P ... 3 (R l 2 —R B 2 ) 0 o+ 6 RcP 1 

Po{0) ~ 4PF + 2P0 2 

(0) 

GPo(0 

The coordinates of any point 
on this line show what coinci¬ 
dent values of a pressure in 
the bore. Pa, combined witli 
an external pressure Pi will 
just bring the inner surface 
of the bore to its elastic limit 
of circumferential strain. 

„ , , 3(Pr-P. :! )po+2PrP I 

<«> 

PiPo(p) 

Similar to the above for the 
elastic limit of radial strain. 

















































28o 


Naval Ordnance 


Principle of the diagram for three cylinders.— 

Axes are drawn as indicated in Fig. 53, in the upper right- 
hand quadrant, of which is constructed, for the tube considered 
as a cylinder subjected to internal and external pressure, a dia¬ 
gram similar to Fig. 39. In the second quadrant is constructed a 
similar diagram for the jacket considered as a tube subjected to 
internal and external pressures. 


Pressures' 
at the 

second V 
contact 
surface „ 


Jacket. 


Pressures at first 
contact surface 

*- - - > 


A 


o 

3 


Tcbe. 




O 



Pi 

■*-> 

'ai 

Pi 


Pi 

2 

h 

CJ 

■*-> 

£ 

h 

a> 

H 

P, J J 

r p ‘ 

Pi 

91 

M 








aO 

* 




O 





& 




f p . 





p { P : 



P 0 


External to Jacket 



Internal to Tube 

Internal to Hoop 



TPressures 
P in the 
0 \bore 


Fig. S 3 . 


For the hoop, only one calculation is necessary, that, P 2 ( 0 ) 
beyond which the internal pressure of the hoop must not be carried 
without exceeding the elastic limit of circumferential strain. 

For the sake of clearness, the line P 1 S l of Fig. 48 is in Fig. 53 
plotted in the first quadrant, while the corresponding line P-S 2 
for the jacket is dropped to the third quadrant. 

For any assumed condition of the hoop, jacket, or tube, coinci¬ 
dent relationship of the other parts may be traced through the 
diagram, and effect of modifying one element noted in the others. 

The first lines drawn are P 1 P 0 {6), P l P 0 (p), P 2 P 1 (d), P 2 P 1 (p), 
p x P 0 , and p 2 p x , as given by the equations assembled above. Read 
Fig. 54 in connection with what follows. 











Pressures and Shrinkages of Built-Up Guns 281 

I he next step is to assume that the system is in action and that 
the hoop has been brought to its allowable elastic limit as given. 
The pressure which will do this is P 2 ( 0 ). 

Next, with P 2 ( 0 ), now as an external pressure to the jacket, 
we must find from the line P.P X (6) or P.P x (p) what internal 
pressure we may allow for the jacket. This pressure is usually 
taken as the least given by either of the lines P.,P X (6) or P 2 P x (p). 
Having determined this value of P x we must next find what pres¬ 
sure P 0 in the bore must be used to develop this value of P x . This 
is determined by the points in which the horizontal line drawn 
from the above determined value of P x cuts the lines P,P () (0) 
and P x P 0 (p). 

There will thus be two values for P n which will produce that 
value of P x which in turn produces that value of P 2 which will 
bring both hoop and jacket simultaneously to their elastic limit 
of circumferential strain. 

One, P 0 (p), of the two values of P 0 , acting with P x will bring 
the inner surface of the tube to its elastic limit of radial strain. 

The other value of P 0 , P o ( 0 ), acting with P, will bring the inner 
surface of the tube to its elastic limit of circumferential strain. 

* If P o (0) as determined above be less than P 0 (p) then the latter 
will be disregarded, for we may not admit in any case, that the 
elastic limit of circumferential extension can be safely exceeded 
for any part of the system. 

If. however. P o ( 0 ) as determined above be greater than P„(p), 
there will be two possible values of P„, which will lead to different 
results as one or the other is adopted. 

Simply stated, when P„( 0 ) >P„ (p), it will require larger 
shrinkages to produce the required value of P t with a value of 
P 0 = P 0 (p), than it would with a value of P o = P o ( 0 ). 

As reduced shrinkages produce less strain for the state of rest, 
and as this is desirable, let us base the shrinkages, with which 
the cylinders are assembled, upon P„ = P I) (6). 

Having now decided upon P.,, P x , and P 0 , assume that the 
pressure in the bore disappears and that the gun gradually reaches 
a state of rest. 

P 0 will become o; P x becomes 2 P X = (P x + /q), and P 2 become 
P... Pj will fall along a line parallel to the line /qP„ and P., will 

* Birnie, Ord. Notes U. S. A. No. 59. 


282 


Naval Ordnance 


fall parallel to the line p 2 p x , stopping at that value of P 2 as deter¬ 
mined by 2 P x as an internal pressure on the jacket. 

From the above value of P . 2 and the line P 2 S 2 , we get S 2 ; and 
from the same value of P 2 and the line p x P 2 we get p x . Deduct¬ 
ing p x from 2 P x we get P x , and with this and the line P X S X , we 
get S x . 

If in the state of rest 2 P x be equal to or less than 2P 1 (max.) 
the tube is not overcompressed at the bore and the gun is safe. 
If, however, 2F t be greater than 2P 1 (max.) we must readjust 
the values of S x and S . 2 so as to make the bore safe from over¬ 
compression for the state of rest, or better, select an allowable 
value of 2 P x and from this determine S x , S. 2 . P t) , etc. 

Each one of the foregoing steps may be performed graphically 
and is indicated in Fig. 54, in sequence, by the lettering a, b, c, 
d, etc. 

In this figure it will be seen that pressures P 0 = Oc' = P 0 ( 6 ), 
P x = Ob'=P x ( 0 ), and P 2 = Oa = P 2 (6 ) will bring the tube, jacket 
and hoop, simultaneously to their elastic limits of circumferential 
strain. Also, that the shrinkages based on these values are S 2 = Og' 
and S x = Oi. Also, that the pressure at rest at the second contact 
surface is P 2 — dc and 2 P x — Od. By drawing a line from cj)arallel 
to P.,p x , we graphically deduct p x = df from %P X leaving P x — Qf, 
with which value of P x we use the line P X S X to find S x = Oi, as 
stated above. 

271 . A note on the line p.,p,.—This line, to be strictly correct, 
should be drawn from the point d, Fig. 54, as P 0 , p x , and p 2 
should simultaneously become O for P () — 0 . But as this would 
necessitate a new line every time the point d shifted, and as the 
real use of the line is merely to express the degree of the change 
in p 2 for a change in p x , it is sufficient to draw it once for all 
through the origin and use it in the sense of a direction cosine. 

272 . Fig. 55 gives the following information, as shown by the 
construction : 

If, with P 2 ( 0 ) =4.389, we use P x (p), the corresponding value 
of P„(( 9 ) will be 25.04 tons, its maximum possible strength. With 
the same value of P 2 ( 0 ) and restricting ourselves to P X (Q) for 
reasons given in the previous text, we find that P 2 — 4.389, 
P x — 13445, and F 0 = 2 3-33 will just bring the three cylinders 
simultaneously to their elastic limit of circumferential strain. 


Pressures and Shrinkages of Built-Up Guns 



Fig. 54. 










Naval Ordnance 


284 

With these values of P 2 , P x , and P 0 the pressures at rest are 
2 P X = 4.785, P 2 — 2.70, and P x slightly less than 3.0 tons. The 
corresponding shrinkages required are IN =.0210 and N^.0118. 

If for practical purposes vve adopt the values to the nearest 
one-thousandth of an inch thus retaining IN = .021 and making 
S x = .012, P x becomes 3.0 tons, 2 P x 4.85 tons, and P 0 (6) becomes 
23.4 tons. 

If we now call P 0 (p ) our safe limit of pressure in the bore 
P 0 (p) = 18.14, and when this pressure is exerted in the bore the 
pressures at the contact surfaces rise to 11.6 tons in the jacket 
and 4.0 tons in the hoop, returning at rest to 4.85 tons and 2.70 
tons, respectively. 

If it became necessary in assigning shrinkages to adopt 
.S\ = .oo8" and 6' 2 = .oi 6", the corresponding value of P„( 0 ), P x 
and P., would be 2o\, 10.94, and 3.5 tons, respectively. The pres¬ 
sures at rest would be ^=1.98, P 2 = 2.06, 2P, = 3.38. 

If we limit the pressure in the bore by the value of P 0 (p) cor¬ 
responding to P n ( 0 ) =2oN we will have the safe internal pressure 
in the bore = P 0 (/a) = 17 tons ( ± ). 

If instead of adopting the values just considered we had as¬ 
signed 5 ' 1 = .oi5, and IN = .025", the construction clearly shows 
that in action a pressure in the bore of 16 tons would quickly bring 
the hoop to its elastic limit of circumferential strain before the 
elastic limit of either jacket or tube had been reached. 

It shows also that these shrinkages are really unallowable be¬ 
cause 2 P x , due to them, is greater than 2P 1 ( niax -)» an d th e bore 
Is overcompressed in the state of rest. 

The effect, of varying one or both shrinkages, on the working 
of the gun is clearly indicated by tbe figure. 


CHAPTER VII. PLATE I. 



m »mtm **•>”/’•*'* * ^ 

O * . —— 


xxii *4 zr jjfc" 


. 0 Z/o' z S x ns Jetermz 7 ie<i. 

>u 72 &J* 23.33 

0 7 uS’ 


EQuAT/on 3 oseO IN 

PLOTT //V fl— 

rM- +*<39 


Pi») « 7.9B- M47 ?L 

T</>J. 72.03 y .6x6 9 7J 

Pc 16) r £8/0 * I.1XJ E 

Z? </>), 10.71 y.6-fze Z? 

/3, = 0 37'/ Pc 

/>! -0/933 p. 

y t * 0 . Oo4ojP 

S z = 0. 00776 3- p 

fi. ~ 0.6774 ?, 

\P/rw*x)= 373-6 


CkAPVUC T^EP RESENTftT »0H 

°£_1*LE, 

^ ELAHOH pj O^R\NKAGcE Pr ESSuRES 

if* Built-up Guns 

states ofr tVcTvo^ o.tu1^e.st. 

5 -wcK Iticlv . 5 ecKortT. 

%»~3.So 8 lQ-2.5\ vnchas 

Xo-0 , 9|.p,= Zl.S~ ^ 9 t _-p t _,z / i.o ) toii^ y u /^ 

































































































































































































































CHAPTER VIII. 

METALS USED IN ORDNANCE CONSTRUCTION. 

Definitions. 

273 . Stress and strain. —When a force is applied to a body, the 
effect produced depends upon whether or not the body is free to 
move. A force applied to a free body produces motion. A force 
applied to a fixed body produces change of form. (See Art. 177T 

Stresses are of different kinds, depending upon the manner of 
application of the force, as tensile, compressive or torsional stress. 

A torsional stress is a compound stress, and may be resolved 
into a (C tensile stress” on some elements of the material and a 
" compressive stress ” on others. 

Each kind of stress produces a corresponding strain, or effect 
on the material: The tensile stress produces elongation; the com¬ 
pressive stress, compression. Since all stresses may be resolved 
into tensile and compressive stresses, all strains may be resolved 
into elongation and compression. 

274. Elasticity, elastic strength, modulus of elasticity, set.— 
The elasticity of a metal is the property it possesses of resisting 
permanent deformation when subjected to a stress. 

All experiments and experience agree in establishing the five 
following laws for cases of simple tension and compression, which 
may be regarded as the fundamental principles of the science of 
the strength of materials : 

(1) When a small stress is caused in a body, a small deforma¬ 
tion is produced ; and on the removal of the stress, the body springs 
back to its original form. For small stresses within the “ elastic 
limit,” then, materials may be regarded as perfectly elastic. 

(2) Under small stresses the strains are proportional to the 
forces which produce them (Hooke s law), and the ratio of stress 
to strain is a constant for any given material (1. e., Modulus or 
Coefficient of Elasticity). (See Arts. 181 and 184.) 

(3) When the stress is great enough, a deformation is pro¬ 
duced which is partly permanent; that is, the body does not spring 
back entirely to its original form on removal of the stress. This 

285 


286 


Naval Ordnance 


permanent part is termed a set. In such cases, the deformations 
are not proportional to the stresses. It is a fundamental law of all 
engineering- construction that materials be not strained beyond the 
elastic limit. 

(4) When the stress is greater still, the deformation rapidly 
increases, and the body finally ruptures or fractures, and actual 
division of the solid occurs. The maximum stress a material will 
stand without fracture is called its ultimate strength. 

(5) A sudden stress, or shock, is more injurious than a steady 
stress, or than a stress gradually applied. 

The words “ small ” and “ great,’’ used in stating these laws, 
have very different values and limits for different kinds of mate¬ 
rials and stresses. 


General Remarks on Metals. 

275 . Physical properties of metals.—Metals have certain prop¬ 
erties, which are of great importance in the case of metals used in 
gun construction. These principal properties are malleability, 
ductility, hardness, toughness, tensile strength, and elasticity. 

(r) Malleability. —A metal is said to be malleable when it may 
be permanently extended in all directions without rupture, by 
pressure (as in rolling) or by impact (as in hammering). 

(2) Ductility. —A metal is ductile when it may be extended 
permanently by traction, as in wire drawing. Only malleable 
metals are ductile, but their ductility is not necessarily in the same 
ratio as their malleability. 

(3) Hardness. —A metal is said to be soft when it yields readily 
to compression without fracture, and does not return to its original 
form on the removal of the compressive stress; and on the other 
hand, a metal is said to be hard when it does not yield readily to 
compression; that is, when the ratio of the compressive stress to 
the permanent strain produced is very great. The terms hardness 
and softness, however, are only comparative when used in de¬ 
scribing metals; thus, we have hard and soft leads, while any sort 
of lead is soft as compared with wrought iron, which latter is 
called soft when compared with cast iron. 

(4) Toughness in a metal is a relative term to express the 
power of resisting fracture by bending or torsion, and is measured 
by the number of times to which a definite section of the metal 


Metals Used in Ordnance Construction 


2S7 


can be bent through a certain angle on either side of the perpen¬ 
dicular without any fracture. 

(5) Tensile strength. —The tensile strength , or ultimate 
strength, of a metal is the unit stress required to produce fracture. 
Thus, if a bar whose cross-section is A breaks under a tensile 

. . p 

. stress P, the tensile strength of the material is—p 

276 . Hardening.—When steel is heated to a red heat and sud¬ 
denly cooled, for example, by plunging it in cold water, it is 
hardened. The more sudden the cooling, the greater is the hard¬ 
ness attained. Thus, cooling in water gives a greater degree of 
hardness than cooling in oil. The term usually employed to ex¬ 
press rapid cooling of heated steel by plunging in water or oil is 
quenching. It results in an increase in tensile strength and elastic 
limit, but with a corresponding decrease in toughness. The steel 
becomes hard and brittle. 

277 . Tempering.—Tempering is the process of mitigating or 
“ letting down ” the hardness of steel after quenching. It is 
brought about by careful and gradual reheating to a temperature 
of 200° to 300° C., depending on the degree of temper required, 
and then immersing in oil or water, or cooling in the air. I his 
reduces the brittleness caused by quenching, removes some of the 
hardness, and increases the toughness of the steel. 

278 . Annealing.—Just as tempering lets down somewhat the 
extreme hardness and brittleness of steel that has been quenched, 
so heating to a low red heat and then allowing the steel to cool 
slowly removes all the hardness induced by the original quenching 
process. This removal of hardness and brittleness by reheating 
and slow cooling in known as annealing. Not only does it soften 
the metal, but also it relieves any internal strains caused by work- 
ing or quick cooling. 

279 . As we are now especially interested in the metals used in 
gun, armor, and projectile making (steel and nickel-steel), only a 
brief mention will be made of the others. 

280 . Copper, in its pure state, is too weak and soft for con¬ 
struction purposes. It is used for rotating bands of projectiles, 
and for electrical fittings and wirings. 

281. Bronze, an alloy of copper and tin, is expensive, is too soft 
for the bores of large rifled guns, is injured by the heat of high 


288 


Naval Ordnance 


charges, and is liable to flaws due to the segregation of its con¬ 
stituents. It is very ductile, is tough, but is low in elastic limit 
and tensile strength. It is now used for minor parts subject to no 
great strain, as sight brackets, hand wheels, liners and bushings to 
avoid the wear of steel against steel, etc. 

282 . Brass, an alloy of copper and zinc, is used in parts of the 
minor attachments, such as the firing connections, and for cartridge 
cases, primers, etc. 

283 . Cast iron is cheap, easily worked, but of low elastic limit 
and tensile strength. It can be fused and cast without difficulty, 
and is comparatively hard. It is not malleable, and cannot be 
welded, and is brittle. Castings are very uncertain in character, 
due to the method of manufacture. Many, apparently perfect on 
surface inspection, develop serious flaws in machining, and have 
to be rejected. Cast iron is not now used for either guns or 
mounts. 

284 . Wrought iron is almost infusible, but is readily welded. 
Its tensile strength and elastic limit are low; but on account of its 
ductility, it requires a large amount of work to extend it from its 
elastic limit to fracture, which makes it a comparatively safe 
material to use because it will give evidence of weakness before 
actual fracture takes place. The bores of wrought iron guns 
have been permanently indented or bruised by moderate powder 
pressures, the metal not being hard enough. This is a serious 
defect under the high pressures modern guns must stand. 
Wrought iron is no longer used in either guns or mounts. 

285 . Cast steel has a higher tensile strength and elastic limit 
than wrought iron, hut not so great a ductility. As forged steel is 
used exclusively in the manufacture of modern naval guns, so cast 
steel is used for mounts, and it is only the ability to obtain steel 
castings reasonably free from dangerous flaws that has made the 
strong, compact, modern naval gun mount possible. The only 
difference between cast steel and forged steel is that the latter has 
been ivorked, either by hammering or by pressing, which results 
in a rearrangement of the molecules and a marked improvement 
in the physical qualities. But it is also possible to effect consider¬ 
able improvement in the physical properties of steel castings by 
treatment, that is to say, by annealing and tempering. 

286 . Forged steel combines more good qualities for use in 
modern guns than bronze, cast iron, wrought iron, or cast steel. It 


Metals Used in Ordnance Construction 289 

is easily fused, is malleable, and is more or less weldable, according 
as it is soft or hard. It is tough and elastic, with a much higher 
elastic limit and tensile strength than wrought iron or cast steel. 
Its elastic limit, or elongation within that limit, is much higher 
than for the other metals above noted; and this quality makes it 
especially suitable for gun making, in view of the strains which 
are set up in guns by heavy charges. 

287. The properties of wrought iron are not sensibly modified 
by temper, which is ordinarily expressed by saying that wrought 
iron does not temper. Pure wrought iron contains no carbon at 
all; commercial iron may have as much as .30 per cent carbon. 
Soft or extra low steel may contain as low as .15 per cent carbon ; 
there is, however, a great difference in the physical qualities of the 
two metals, due to the methods of manufacture. 

288. Steel proper may be said to contain from .20 per cent to 
2.00 per cent carbon, and cast iron from 2.00 per cent to 5.00 per 
cent. The properties of certain cast irons are considerably modi¬ 
fied when, after having been liquefied, they are cooled suddenly; 
therefore, we may say, from this point of view, that cast iron 
takes temper like steel. 

289. To state in a few words the characteristics which may 
serve to distinguish wrought iron, steel, and cast iron, we may say : 
Wrought iron is forgeable, weldable, practically infusible, and does 
not temper; steel is forgeable, weldable, fusible, and takes temper ; 
cast iron is neither forgeable nor weldable, it is relatively very 
fusible, and is susceptible of being tempered. 

Steel in General—Composition of Steel. 

290. Definition of steel.—Reasoning from the foregoing, steel 
is a fusible, malleable alloy of iron produced in any way -whatever, 
and containing a smaller proportion of carbon or other hardening 
element than is contained in cast iron, and is capable of receiving 
temper. 

291. Process for obtaining cast steel.— 1 here are a variety of- 
processes for removing a portion of the carbon from cast iion and 
producing steel, among which may be mentioned : (1) Melting in 
crucibles, giving crucible steel; (2) melting in the electric furnace, 
giving electric furnace steel; (3) melting in the Siemens or 
Siemens-Martin open-hearth furnace, giving open-hearth steel; 
(4) blowing air through molten cast iron in the Bessemer con- 


20 


290 


Naval Ordnance 


verter, producing' Bessemer steel. In whatever way made, the 
material is essentially the same, depending for its properties upon 
its chemical composition and physical structure. 

The various processes of making steel mentioned above are all 
described in detail in works on Mechanical Processes. No de¬ 
scription of the methods, therefore, is given here. 

292 . High and low steel.—In consequence of the extension 
given to the word steel, we have to-day under this name metals 
which present differences as regards both composition and physical 
properties. Hence, the different varieties of steel have been dis¬ 
tinguished by the proportion of carbon they contain—sometimes 
by percentage, and sometimes by more or less characteristic names. 
When the metal contains a large proportion of carbon, it is ordi¬ 
narily called high or hard steel. If the proportion of carbon is 
small, it is called lozv or soft steel; if still smaller, extra low steel. 
In some manufactories, for example, the name of low steel is given 
to a metal containing .20 to .25 per cent of carbon, and a metal in 
which the proportion of carbon is less than .20 per cent is desig¬ 
nated extra lozv steel. 

All steel contains more or less carbon, together with varying 
amounts of certain other elements, the principal ones being man¬ 
ganese, sulphur, phosphorus, silicon, copper, and arsenic. Of 
these elements, sulphur and phosphorus especially are kept as low 
as possible, since their presence is detrimental to the steel. Certain 
other elements are sometimes found in the iron ore used in mak¬ 
ing steel, or are added as alloys, in certain definite quantities, with 
the object of giving desired qualities to the product; among these 
are: Nickel, vanadium, chromium, aluminum, tungsten, molyb¬ 
denum, uranium, and titanium. Steel containing carbon and ele¬ 
ments of the first group mentioned is usually called carbon steel; 
if it contains, in addition, some one or more of the elements of the 
second group, it is called an alloy steel, as nickel steel, chronic 
steel, etc., depending on the element or elements present. 

293 . Physical properties—how obtained.—The physical prop¬ 
erties of any steel depend on: (1) Chemical composition, (2) 
heat treatment, (3) the amount and kind of mechanical work tc 
which it has been subjected. 

(1) The chemical composition of steel influences both its physi¬ 
cal properties and its structure, owing to the definite compounds 


Metals Used in Ordnance Construction 


291 


formed by the combinations of carbon, manganese, sulphur, phos¬ 
phorus, and other constituents. 

(2) Heat treatment includes the whole of the thermal condi¬ 
tions through which the metal is passed, and embraces both heating 
and cooling by different methods and under different conditions. 

(3) Mechanical work to which the steel is subjected consists 
in rolling or forging to reduce the ingot to the desired shape and 
to impart to it the desired qualities. 

Steel for Ordnance Purposes. 

294 . Castings.—Steel castings for ordnance purposes are used 
chiefly for gun yokes, sight brackets, and the various parts of gun 
mounts. They are produced by either the open-hearth or the 
electric process, the object in either case being to obtain a steel 
that is reasonably free from injurious elements. The excellence 
of steel castings is largely determined by the method of casting. 

295 . Gun forgings.—In the manufacture of steel for gun forg¬ 
ings, the Krupp works in Germany originally used the crucible 
process ; later they adopted the electric process. In the United 
States the open-hearth process has been, and is still, extensively 
used, though at present a great deal of steel for gun forgings is 
made in the electric furnace. 

The crucible process has many advantages in obtaining steel of 
great purity, but on account of the impossibility of insuring 
identical composition in all crucibles, uniformity of composition 
cannot be obtained in ingots of the size required for large gun 
forgings. In the open hearth or the electric furnace, on the other 
hand, a single charge equal to the combined contents of a good 
many crucibles, can be melted down, producing a molten mass of 
• steel of homogeneous composition and a high degree of purity, 
and of a quantity sufficient to produce the large ingots necessary 
for gun forgings. 

Carbon steel is used for certain gun forgings, notably liner 
forgings and some of the outer hoops of large calibei guns. W hen 
so used it is generally spoken of as gun steel. Alloy steel is used 
for the tube, the jacket, and certain hoops—chiefly those directly 
over the tube and jacket—which are subjected to the most stress 
on firing, and require material of high-tensile strength and elastic 
limit. The particular alloy used is nickel, producing nickel-steel 


Naval Ordnance 


292 

forgings. A chrome steel is avoided in gun forgings for the 
reason that it is too brittle and is liable to crack on shock of firing. 
The following table gives the average chemical composition of 


gun forgings: 

Gun Steel. Nickel Steel. 

Carbon .50% .40% 

Manganese .70 “ .70 “ 

Silicon .. .27 “ .27 “ 

Phosphorous .03 “ .03 “ 

Sulphur .03 “ .03 “ 

Nickel.. 300“ 


296 . Armor.—The armor used on ships of the U. S. Navy is 
face-hardened, excepting the plates for turret and conning-tower 
tops, which are of special-treatment steel. Face-hardened armor 
is designated as Class A, and the special-treatment steel plates as 
Class B. 

Protective-deck plating and splinter bulkheads are made of 
special-treatment steel, but are not classed as armor. 

Class A armor may be cemented or non-cemented. For non- 
cemented armor the carbon content is somewhat greater than for 
cemented armor. The composition is predetermined, being low- 
carbon steel, containing inseparable ingredients of phosphorus and 
sulphur, the percentage of which it is endeavored to keep at a 
minimum, and nickel, chrome, silicon, and manganese. (See Art. 
58 /.) 

297 . Projectiles.—Steel for projectiles is made by the crucible, 
open hearth, and electric processes. (See Art. 646.) 

298 . 

Recapitulation. 

Purpose. Kind of steel 1 used. 

(1) Gun-mounts, yokes and Alloy steel castings. 

sight brackets. 

(2) Guns.Gun steel forgings for liners and outer 

hoops of large caliber guns. 

Nickel steel forgings for tube, jacket, and 
inner hoops. 

(3) Armor .Class A,—Alloy Steel, pressed or rolled. 

face-hardened. 

Class B,—Special-treatment alloy steel, 
pressed or rolled, not face-hardened. 

(4) Protective deck and Special-treatment alloy steel, pressed or 

splinter bulkheads. rolled. 

(5) Projectiles .Alloy steel, forged. 











Metals Used in Ordnance Construction 


293 


Method of Manufacture of Steel and Alloy-Steel Gun Forgings. 

299 . Furnace practice.—Nickel-steel and gun steel for gun 
forgings are made in acid open-hearth furnaces and in electric 
furnaces, because of the increased probability of blowholes and 
gas bubbles in steel converted by the basic process, due undoubt¬ 
edly to the fact that such steel is likely to be more highly charged 
with oxygen. The furnace charge is made up of about one-third 
pig iron low in phosphorus and about two-thirds plain or nickel- 
steel scrap, such scrap being parts of old ingots, cuttings, and 
turnings. The exact proportions of pig and scrap depend on the 
quality and quantity of the scrap obtainable, and also on the 
analysis of the pig iron (particularly its silicon content) ; but the 
pig iron generally constitutes from 20 to 30 per cent of the charge. 
The scrap, if the product is to be nickel-steel, contains from 2 to 
2i per cent nickel. From six to eight hours are required to bicak 
down and thoroughly melt the charge, and as soon as this occurs 
samples are taken. A fracture test enables an experienced person 
to closely estimate the percentage of carbon contained in the 
charge. Other samples are sent to the chemical laboratory, where 
analysis is made for carbon, manganese, silicon, sulphur, phos¬ 
phorus, and nickel. The nickel is not oxidized, and remains con¬ 
stant, and the amount to be added, if any, is determined from the 
analysis and introduced in the form of pure nickel blocks or 
“ plaques.” 

Every half-hour after the charge is melted a carbon test is 
made, until the carbon has been reduced to the desired percentage 
by oreing down. This consists of adding iron ore from time 
to time, Lake Superior hematite being generally used, the reaction 
being Fe 2 0 3 + 3C = 2Fe-|-3C0. For nickel-steel tubes and liners 
the carbon is reduced to between .35 per cent and .42 per cent, but 
for “ gun steel ” the amount of carbon will run between .42 pei 
cent and . per cent. From the results of the analyses the various 
necessary additions are made to bring the manganese and chro¬ 
mium up to the required amount. Ferro-manganese, or spiegel- 
eisen, is added to increase the carbon and manganese, the former 
being used when a smaller increase of carbon is desired. Ferro- 
chrome is added if necessary. Loam is put in to increase the slag, 
limestone to thin the slag. 


294 


Naval Ordnance 


From io to 20 hours after the bath is melted, it is tapped into 
ladles. Ferro-silicon is added to the ladle to bring the silicon up 
to the required amount. The molten metal is allowed to run into 
a large refractory-lined ladle, and as the tap hole of the furnace 
is below the slag line, only a small amount of slag goes into the 
ladle, and this remains at the top ; by using bottom-pouring ladles 
the amount of slag is still further reduced. 

300 . Ingots.—Two kinds of ingots are used—the corrugated 
ingot for gun forgings and the fluid-compressed ingot. The ingot 
molds are tapered from top to bottom, the top being smaller. The 
size of the ingot is its diameter at the middle of its height. The 
ingots are top- or bottom-poured indifferently; some manufac¬ 
turers top-pour all ingots, others bottom-pour, and some one-half 
bottom-pour and one-half top-pour. A tong hold is left at the top 
of ingots to assist in handling, which also serves as a sink-head to 
take care of most of the slag, segregation, and piping. 

301 . The Whitworth process of fluid compression frees the 
cylindrical ingot of much of its gas content and thus reduces the 
amount of blowholes and piping. The liquid metal is subjected to 
slowly increasing pressure until about 2300 pounds per square 
inch is reached. This pressure is held for four or five hours, or 
until the metal has entirely solidified. 

The last samples, three in number, are taken during the pouring 
of the ingot; two are analyzed for carbon, manganese, silicon, 
phosphorus, sulphur, and nickel, and the result of the analyses 
is sent to the forge, where it is used in determining the forging 
heat. The third sample is taken to a small forge near at hand and, 
without treatment, is forged into test bars to ascertain the approxi¬ 
mate physical qualities; this, known as the “ heat test,” gives an 
idea as to what can be expected of the metal. 

As soon as the ingot is cold enough, it is stripped from the mold 
and a number is placed on it; this number remains with it for 
identification until it has passed through all of the processes and 
forms a part of a finished gun. The ingot is immediately taken to 
an annealing furnace, where it is slowly and uniformly heated. 
Soft coal is used for heating, and the furnaces are provided with 
baffle walls for protecting the ingot from the direct action of the 
flame. The ingot enters the furnace at a temperature of about 
1400° F., and is kept at this temperature for about five hours, after 


Metals Used in Ordnance Construction 


295 


which time the fires are allowed to die down and the ingot cools 
slowly with the furnace. From three to four days are required for 
the cooling of a large ingot. 

The ingot is now sent to a machine shop, where it is slung on a 
large lathe, and the specified amounts of top and bottom discard 
are removed. If the ingot is to be used for hollow forging, it is 
put in a boring mill and rough-bored to the required diameter. 
After the discard has been removed, and after boring (if this 
operation is required), the ingot, if not to be forged in one piece, 
is cut into blocks of the required sizes. This is done in the lathe 
used in cutting oft" the discards. 

A separate number is stamped on each block made from an 
ingot, using the ingot number as the first part, and following it 
with letters and numbers to indicate the relative position of the 
block in the ingot. These numbers always begin at the breech or 
bottom end of the ingot; thus, if ingot No. 12345 were cut into 
four pieces, the bottom block would be No. 12345B1, the second 
block from the bottom No. 12345B2, and so on. If the whole 
ingot, after discards have been removed, is to be used in a single 
forging, it carries its ingot number and is designated Bi. If any 
of these blocks are afterwards cut into smaller pieces, the number 
given these pieces would be No. 12345B1F1, No. 12345B1F2, etc., 
numbered from breech end of block. (The ‘‘ F ” stands for 
“ forging.”) 

Before leaving the machine shop the block is examined by a 
sub-inspector for signs of piping, blowholes, and other defects, 
and the amount of discard is checked. 

302 . Forgings.—Forgings for pieces whose finished interior 
dimensions are small are forged solid ; larger pieces are bored 
before being forged. For instance, the tube and jacket and “ B ” 
hoops of a 14-inch gun would be forged solid; the “ C ” and “ D ” 
hoops would be bored before being forged. 

From the machine shop the block is taken to the forge, where it 
is brought to the desired forging temperature in an acid-lined 
regenerative, producer gas furnace, or other similar furnace. This 
temperature is usually about 2100° F. If the block is a long one, 
one end is heated at a time; the other end, projecting from the 
furnace, is used for handling the piece during the forging oper¬ 
ations, the ends being alternately heated and forged under a 


296 


Naval Ordnance 


hydraulic press. Small blocks go entirely in the furnace, and are 
heated uniformly. The length of time required to bring the block 
to forging heat depends on the size of the block, and the quality of 
the steel. Great care is taken not to heat too rapidly, this being 
particularly important with alloy steels. 

The block having been brought to forging heat, it is balanced by 
means of a porter bar, and taken by an overhead crane to the 
hydraulic forging press. There the operation depends upon the 
kind and shape of forgings to be made. 

ff to be forged solid, the block is forged down and drawn out 
by repeated workings, the forging being supported in a V-shaped 
anvil under a slightly concave die secured to the tap or head 
of the press, the pressure being applied gradually for about three 
seconds, with about one-second intervals between pressures. As 
the forging operation is generally discontinued when the block has 
cooled to about 1550° F., several heats are necessary for tubes 
and liners. 

The hollow forgings are forged on a mandrel which snugly fits 
in them. The forging is done as above described, between the 
V-shaped anvil and concave tup, as in the case of solid forgings; 
and in this manner the hole is not enlarged, but the wall thickness 
is reduced, and the metal is drawn out along the mandrel. With 
large forgings about eight heats are required for this operation, 
the mandrel being removed each time before the forging is put 
back in the furnace. 

Short hoops of large diameter are forged on an enlarging bar, 
the ends of which are supported on rests, or jacks , on each side of 
the press, with the forging hanging free on the bar between them 
and under the tup. By this means the thickness of wall is reduced 
and the hole enlarged without an appreciable change in the length 
of the forging. If it is necessary to lengthen a hoop thus enlarged, 
a mandrel is used for drawing it out as explained above. 

Breech bushings, or screw-box liners, are first forged or drawn 
down before being bored. Thus, a forging of this kind for a 12- 
inch or 14-inch gun is made from an 84-inch corrugated ingot, 
forged down to a diameter of 54 inches, annealed to relieve it of 
forging strains, bored through the center, heated for reforging, 
put on an enlarging bar, and the hole enlarged to the required 
dimensions. As these bushings are made, of nickel-chrome steel, 


Metals Used in Ordnance Construction 


297 


which is very apt to crack while under the press, they must be 
carefully nursed, and two or more reheats are necessary—one 
called the shaping heat, and one the finishing heat. Large breech 
bushings are always forged in pairs with their breech faces 
together, each end of the forging being forged down in steps as 
required by the drawings. After forging and subsequent anneal¬ 
ing, they are cut apart in the lathe before being sent to the treat¬ 
ment department. 

When the forging operation has been completed, the manufac¬ 
turer sends a forging report and sketch of the rough forging to 
the inspector. The report contains the order number, drawing 
number, description of article, forging number, weight of discard, 
top and bottom, and size of bore. Ihe sketch shows the general 
shape of the forging, with dimensions, and from this the forging 
reductions are figured. 

From the forge all gun forgings are returned to the annealing 
furnace, and there annealed at a high temperature (about 75 0 
above critical) for a considerable length of time to remove strains 
and to break up the previous structure. This annealing is done 
generally in an oil furnace. A button is taken and examined 
under the microscope to determine whether the metal is ready for 
tempering. 

303 . Machining.— After annealing, the forgings are sent to the 
machine shop, where the rough ends are cut off, steady rest beat¬ 
ings turned, and the scale removed. If a solid forging, it is put in 
a boring lathe and bored out to about 1 inch less than finished 
dimensions. When these operations are completed, the forging 
is examined for cracks, signs of piping, or other defects. From 
the machine shop the forging is sent to the treatment department. 
On short pieces sufficient metal is left on the inside and outside to 
allow for warping in treatment; on larger pieces the forgings are 
machined to the required rough forging dimensions, and if warped 
in treatment are straightened under a press. Sufficient excess 
metal is left on each end of the forging to provide test specimens 
required by the specifications. 

304 . Treatment—tempering and annealing. I he method of 
treating and annealing the forgings, and a general description of 
the furnaces used by one of the larger manufacturing plants, are 
here given without any attempt to discuss the theory of heat treat- 


298 


Naval Ordnance 


meat or special processes or details. Gun liners, tubes, and hoops 
are lowered vertically by means of holding rods and crane into pit 
furnaces and there brought to heat for tempering. 1 liese pits are 
of various sizes and depths, the largest being 60 feet deep and 70 
inches in diameter. They are lined with fire-brick and heated with 
producer gas supplied through a number of nozzles or tuyeres 
piercing the furnace in rings equally spaced ;-the direction of these 
nozzles being tangential to the walls of the furnace, the forging is 
not exposed to the direct action of the flame. 1 he length of time 
that a forging remains in a furnace depends on the size of the 
forging, its carbon content, and the temperature of the furnace. 
Ten to 12 hours are generally required to thoroughly soak a forg¬ 
ing to the desired temperature. 

The oil wells into which the forging is immediately immersed 
after removal from the furnace are about the same size as the 
heating pits, and are also sunk in the ground. Forgings are 
immersed in the direction of their longitudinal axis. The oil is 
kept continually in circulation by means of a pump which forces 
it up through the bottom of the well, the overflow being carried 
ofif by a pipe at the top to a tank outside the building. After about 
12 minutes have elapsed, the forging is taken out and put into the 
annealing furnace, where it is supported, in a horizontal position, 
on narrow uprights, and gradually brought to the desired tem¬ 
perature. This takes from six to eight hours. The annealing 
furnaces are heated with producer gas, and the forging is pro¬ 
tected from the direct action of the flame. Self-recording 
pyrometers are used for measuring the temperatures. After being 
brought to proper heat, the forging is allowed to cool slowly. 
This is accomplished by a complete or partial reduction of the 
flame, as may be required, depending on the condition of the fur¬ 
nace. When cooled to about 300° F., the forging is removed from 
the furnace. 

When entirely cool, the forging, if a tube, liner, or long hoop, 
is tested for straightness ; and if warped enough to make this oper¬ 
ation necessary, it is again heated (not over 850° F.) and straight¬ 
ened. It is then re-annealed from a temperature slightly above 
that given it for straightening. The forging is now ready for the 
company’s test. Trial bars are taken, and if, in the opinion of the 
company, the forging is in proper condition, official submission is 


Metals Used in Ordnance Construction 


299 


made on a form which gives the forging number, description, and 
order number, and on the back of the form the record of the last 
trial tests. Upon receipt of this form the inspector refers to his 
records; and if the treatment of the piece is satisfactory, the 
official test bars are laid out as prescribed by the specifications. 
These bars are slotted out and machined in a special shop, which is 
a branch of the treatment department and wherein only this class 
of work is done. The stamping of test bars and the witnessing of 
the test is done by a sub-inspector. 

305 . Determination of physical properties.—When steel for 
any of the above purposes is produced, tests are made to establish 
its suitability for the particular purpose for which it was intended. 
These tests involve subjecting specimens of the metal to the action 
of different stresses in testing machines, and observing, by means 
of accurate measuring instruments, the deformations produced by 
these stresses. 

306 . Testing machines.—The testing machines are generally a 
combination of levers for recording the stress, and a system of 
gearing or hydraulic machinery by which the stress is produced. 

Specimens are usually prepared to an adopted shape. In the 
case of gun forgings they are cylindrical, and are turned to the 
same diameter for a certain length, usually not less than 2 inches 
and not more than 10 inches for tensile tests ; and in addition, ends 
are allowed for the purpose of attaching the specimen to the 
machine. For compressive tests the specimen is also cylindrical, 
the height being twice the diameter. The capacity of the machine 
limits the diameter of these specimens. 

In making a tensile test, the specimen is marked at two points 
as far apart as the finished length between grips will allow, and 
the length is carefully measured between these points. The 
diameter is also measured by micrometer calipers. It is then 
placed in the machine and subjected to successive tensile stresses, 
the elongation being noted for each stress, both when the load is 
on and after it has been removed. 

307 . Specifications governing the manufacture of ordnance 
material, which are changed from time to time to keep abieast of 
the best metallurgical practices and results, state the physical 
requirements the material must fulfil, and these requirements aie 
carefully checked up by inspections, by analysis, in the testing 
machines, and by various proof tests at the proving ground. 


300 


Naval Ordnance 


308 . A curious and anomalous condition in ordnance require¬ 
ments can be seen by an inspection of the table of strengths for 
gun forgings. 

It will be seen, from this table, that for the forgings of the 
larger guns the hoops are required to be stronger than the jackets, 
and the jackets stronger than the tubes. ’ 

It is desirable that the opposite rule should obtain, and that the 
tube should be the strongest part of the structure. 

Explanation is found in the fact that it is impossible to make a 
large mass of steel as nearly perfect as a small piece. The smaller 
the forging the more uniform its texture and the more readily and 
the more perfectly will it yield to the processes of annealing, tem¬ 
pering, etc., the processes that affect its tensile and elastic strength. 
The Navy Department is forced to recognize these facts in its 
specifications. 


CHAPTER IX. 

DETAILS OF CONSTRUCTION OF NAVAL GUNS. 

309 . The major caliber guns for the naval service are manu¬ 
factured at the Naval Gun Factory and at private plants, such as 
the Bethlehem Steel Co. and Midvale Steel Co., and also at the 
United States Army Arsenal, Watervliet, N. Y. Ihe greater 
portion of the work, however, is done at the Naval Gun bactory, 
and the method of manufacture and inspection in use there are 
herein described. 

Preliminary. 

310 . The following general remarks apply to all main-battery 
guns, and will be followed by a detailed description of the 
assemblage of the 14-inch gun. 

Parts of a gun.— (1) A modern built-up gun is composed of a 
tube and hoops. They are designated as the A tube, and the 
Bi, B2,.. ., Ci, C2,.. ., Di, D2,..., etc., hoops. 

(2) The Bi hoop, usually called the jacket, is immediately over 
the rear end of the tube and extends well forward on it. 

(3) Hoops over the forward part of the tube are called chase 

hoops. 

(4) Hoops over the jacket are called jacket hoops. 

(5) Locking hoops are those which hold two adjacent parts 
together. Inner ones are shrunk on; outer ones may be screwed 
or shrunk on. 

The present tendency is to omit the term “ jacket, using simply 
the term “ hoops ” with the proper designation. 

311 . Receipt and assignment of forgings.—(1) Forgings, 
when received at the gun factory, are weighed and examined for 
the marks required at the steel works and by the naval inspector at 
those works. No work is to be done unless these marks are found. 
The forgings are measured to see if they are of proper dimensions 
to work out to finished drawings ; only .02 inch tolerance is allowed 
over the drawing dimensions for the forgings. An examination 
is made for gouges, etc., and for defects in the forgings which 
would not disappear in the finish machining. 


301 


302 


Naval Ordnance 


(2) All forgings in any gun are from the same steel works, if 
practicable. 

312 . Setting the forging in the lathe.— (1) The forging is 
brought to the lathe by a crane, and one end—the breech end, for 
instance—is gripped by the four to six large jaws on the face 
plate. The muzzle end is likewise gripped by a pot center, a large 
iron ring with several arms screwing through it radially. 

(2) The forging is now on live centers. By revolving the forg¬ 
ing and screwing the jaws of the face plate in or out, the breech 
can be centered, as shown by the mark of a tool on the surface of 
the forging. 

(3) The muzzle end is similarly centered. Then the forging is 
revolved while the tool is run along its carriage. This is done to 
see whether the forging is warped. Should it be warped, the 
screws at each end are moved so that the work is thrown to one 
side or the other to offset the warping. If the forging is so badly 
warped that it cannot be trued up by this means, it is rejected. A 
surface is now turned near the muzzle end for a steady-rest. In 
all long work, one or more steady-rests are used to prevent spring¬ 
ing, and the work must be supported by them in boring. The 
steady-rest is placed in its bearing, and the pot center is removed 
so that the balancing rod can be inserted and the eccentricity of 
the bore be noted. It may be necessary, because of eccentricity of 
the bore, to throw the center a little to one side or the other, but in 
any case there must be sufficient metal both inside and out to work 
out to the finish dimensions. When the direction is finally deter¬ 
mined, the steady-rest surface is trued up, if it has been thrown 
out, and surfaces are turned for additional steady-rests. 

(4) A bearing is also bored out at the muzzle end, in which is to 
he placed a dead center for use in turning. For boring, the work 
is supported in the steady-rests. 

313 . Turning.—All except very short hoops are at once given a 
rough cut, on the outside, to remove the scale and take out the 
spring. This cut is only made deep enough to remove all scale, 
though in the case of a badly warped forging this may require a 
deep cut on one side and a shallow one on the other. In this and all 
turning, the work is revolved while the tool is fed along in its 
carriage Fig. 1, Plate I, shows the forging for a 14-inch tube, 
set for turning. 


CHAPTER IX. PLATE I. 



Fig. i.—14-Inch Tube in Lathe for Turning. 



Fig. 3.—Indicator Mounted on Tool Carriage. 













304 


Naval Ordnance 


This rough cut is the only outside one taken until after the parts 
to go on over the piece have been bored and star gauged and the 
shrinkage sheets made out. Then the turning is continued, some¬ 
times using as many as four tools at the same time on two or more 
carriages. For finishing cuts, tools i to 2 inches wide are used, 
and dimensions are kept correct to .001 of an inch. Steel snap 
gauges previously set by steel points of known lengths are used 
to get the diameters. 

314 . Boring.— (1) For boring short hoops of large diameter a 
boring bar is used. The tool is set on the end of the bar to give the 
proper cut, and fed along by the carriage as the work revolves. 

(2) For long cylinders there would be too much spring in the 
boring bar, and packed bits are used. These are cylinders of oak 
wood, on iron frames, carrying two tools. The wood is a few 
thousandths of an inch larger than the hole to be cut, so that, by its 
forcing, the tools are held rigidly and accurately. Fig. 2, Plate I, 
shows a 14-inch Ci hoop set for boring, with the packed bit used. 

(3) Frequent inspections are made during the boring to see that 
the hole is true, as, owing to wear of tool, spring of metal, etc., 
errors constantly creep in. The bit is first carefully centered in 
the lathe by mounting it on its bar and revolving it while a small 
spring indicator, mounted on a small base, is pressed against it. 
This indicator shows any eccentricity to .001 of an inch. By 
putting liners of thin metal or paper between the stem of the bit 
and the socket in the end of the bar, it is moved until centered. 
Then the cut is started, the bit being run in about 8 inches and 
then withdrawn. The hole is " indicated ” with the instrument 
later described, and is tested with steel points set at right angles, to 
see that it is of the proper diameter. If satisfactory, the bit is 
again entered, and the cut is continued. Every few feet the bit 
is withdrawn and the bore is indicated and tested with points for 
diameter—the frequency of this testing depending on whether the 
cut is a fine or a rough one, and on what the first measurements 
show in the way of accuracy. If the bit is running out consider¬ 
ably, as sometimes happens on the first rough cut, the work may be 
reversed after the cut has gone half way through, and the bore be 
finished from the other end. Any eccentricity may be corrected by 
truing up the bore with a slightly larger bit. Four cuts are usually 
required to finish a bore—two rough and two fine ones. 


Details of Construction of Naval Guns 305 

(4) In boring out cylinders which are stepped and have two or 
more internal diameters, all work, except perhaps the first rough 
cut, as noted above, is done from the end where the diameter is 
largest, usually the breech. After the rough cut has been taken, 
the largest diameter is accurately bored out. A packed hit is then 
prepared with the forward end and tool set at the diameter of the 
smaller hole to be cut, while the after end is left at the larger 
diameter. This bit is run in and the smaller bore is started. The 
bit is then withdrawn and the bore is indicated and star gauged. 

(5) In all boring, the bits are kept well lubricated by oil run 
into the bore. 

315 . Balance rod or indicator.—To ascertain whether a hole 
has been bored true with the line of dead centers, a simple device 
known as a balance rod or indicator is used. This device con¬ 



sists of two wooden rods joined together end-on by a right-angled 
strap of iron. One rod, the one which enters the bore, has a 
small roller on its end. The other rod holds a pointer. The rod 
is inserted in the bore and balanced on a knife edge under the 
iron strap, the roller resting on the bore. A vertical stand is 
placed so as to record the marking of the pointer. A zero point 
is first marked by the pointer, and then the work is slowly revolved. 
Should the hole be eccentric, the pointer will move up or down and 
serve as a means of indicating the amount of eccentricity of the 
bore at the point where the roller is. These indications are taken 
every two feet. A long forging that is being bored will be indi¬ 
cated about three different times during a cut, to see whether the 
bit is running true. Should the bit be running out, the centers are 
thrown and the bore is trued up with a slightly larger bit. After an 
accurate hole has once been bored there is little danger of the bit 
running out in succeeding cuts. (See Fig. 56.) 


21 



















3°6 


Naval Ordnance 


For guns which are set in lathes where there is not room to use 
this type of indicator, another one is used. This, as shown in the 
photograph (Fig. 3, Plate I), is mounted on the tool carriage at 
the end of the gun. A heavy, rigid beam carrying a small wheel on 
its end enters the bore, the wheel resting on the surface of the bore. 
The beam is supported on a knife-edge near its other end, and by 
a system of levers delivers its movement to a pointer traveling 
over a scale. A weight on the pointer rod is used to balance partly 
the beam. The allowable travel of the carriage between the breech 
of the gun and the fixed guide on the lathe for the dead center, is 
only a few feet; so. after indicating part of the bore, the beam is 
replaced by a longer one. This is continued until the entire bore 
has been gone over. 



Fig. 57.—Bore-Searcher. 


316 . Bore searching.— (1) Every forging, when finish-bored, 
is bore searched, and all bore searching is done by officers. The 
bore is also inspected after each cut, by a foreman with an electric 
light. 

(2) The bore searcher is simply a wooden frame, holding a 
mirror inclined 45° to the axis of the bore. Three incandescent 
electric lamps furnish the light, and a hood is provided on the 
frame to obscure the direct light from the observer. The bore 
searcher is moved slowly through the bore by a long wooden 
handle. About 90° of the bore is illuminated at once, and four 
lightings are required completely to search it. 

















• crq 


Details of Construction of Naval Guns 


307 


(3) The bore is inspected for any discoloration, cracks, or 
streaks, or any flaws that may have developed in the boring; opera 
lasses or binoculars are used, if considered necessary, in inspect¬ 
ing long bores. If any flaws are noticed, they may be scratched 
with the pricker, a steel point mounted on a light wooden rod at 
right angles to it, to see that what appears to be a flaw is not merely 
a spot of dirt. 

317 . Star gauge.— (1) The star gauge (Fig. 58) is used to 
measure accurately the inner diameters of any long cylinder. This 
instrument is a graduated brass or steel tube, built in sections so as 




to be adapted to any length of work. It carries a head and a 
handle. 

(2) The head contains three sockets, 120° apart, pressed upon 
a coned rod by springs. Into these sockets are screwed points of 
lengths suitable to the work to be measured. The coned rod is 
simply the extension of a rigid steel rod passing through the tube 
and securing to the handle. Any forward movement of the handle 
moves the cone forward and causes the points to be pressed out a 
known amount, which is read from a scale on the tube and a 
vernier on the handle. 

(3) The star gauge is always adjusted before use by trying the 
points on a ring of known diameter. A set of rings of different 
diameters is supplied with the instrument. By adjusting the posi- 




























3°8 


Naval Ordnance 


tion of the handle the scale is made to read zero when all three 
points just touch the ring. In measuring the diameters of the 
bore the readings of the scale must be applied to the diameter of 
the test ring to get the correct diameters The bore, whether of 
forging or of gun, is star gauged at each inch of length and the 
powder chamber at each half-inch. The points are first set thus: 
® and then a second series of readings is taken with the points 
reversed, thus: 0 

(4) In star gauging the gun, after it has been rifled, guides 
are used on the head. These guides follow grooves and thus 
keep the points always on the same lands or in the same grooves. 
On the muzzles of all our guns the letter “ S ” will be found in 
four places. From the positions of this letter the lands and 



t~ /son -J 

Steel Tomt 

Fig. 59. —Instruments for Measurement of Diameters. 

grooves which were star gauged are known. Double readings are 
taken of both lands and grooves, the second reading being with 
the points reversed. 

(5) The readings of the star gauge are correct to the .001 
part of an inch. The record of every star gauging, whether of 
gun or of forgings, is kept on file. 

318 . Shrinkage.—The shrinkages for the different parts are 
prescribed by the Bureau of Ordnance. They are computed and 
are the same for all guns of a type if the material used in the 
different guns is of about the same strength. The different layers 
of the gun have different shrinkages, and the shrinkage in any one 
layer is not necessarily the same throughout. 

319 . Measurements.— (T) The figured dimensions on draw¬ 
ings are used. The rear face of the tube is taken as the origin for 
all measurements. 














Details of Construction of Naval Guns 


309 


(2) In all machining the workman is furnished with the neces- 
sary gauges, graduated rods, and steel points for the dimensions 
on his drawings. All measurements originate in the measuring 
department, and all gauges are frequently referred there for 
verification. 

(3) I n general, diameters are given in thousandths of an inch 
and lengths in hundredths. Certain tolerances are allowed in 
machining, and these are never exceeded. 

(4) Outside diameters are measured either with snap gauges 
or with beam calipers. Inside diameters, with steel points or the 
star gauge. (See Fig. 59.) 

Building up the Gun. 

320 . Jacket.— (1) The Bi hoop or jacket is the first forging 
worked upon. A rough cut is first taken ofif the outside to remove 
spring, and then the forging is set for boring and bored out to 
exact dimensions. This usually requires two rough cuts and two 
finishing cuts with packed bits. 

(2) The forging is faced ofif, inspected for flaws on the outside, 
and then removed from the lathe and bore searched, any flaws 
being noted. It is star gauged at each inch of length, the gauge 
being run through twice, as noted above. The length is divided 
into four parts by cuts on the outer surface; these distances are 
measured and the outer diameters are calipered. These divisions 
and diameters are again measured and calipered after assembling, 
to note what extension of diameter has been given the jacket, and 
to see if the longitudinal contraction has been uniform. 

(3) The B2 hoop is at the same time prepared for assembling 
by the same processes of machining, inspecting, and star gauging. 
The shrinkage sheet for the tube is then made out as follows: To 
the internal diameters of the Bi and B2 hoops, as found by star 
gauging, are added the shrinkages assigned by the Bureau of 
Ordnance for each point. The resulting measurements are marked 
on a blue-print of the tube, giving the desired external diameter 
of the tube at each point. The tube is then machined. 

321 . Tube.— (1) After a rough cut has been taken from the 
outside of the tube, it is set for boring, and the bore is cut out to 
within .35 of an inch of finished diameter, two cuts with a packed 
bit being required. 


3io 


N A V A L O R n N A N C E 


(2) The tube is again set for turning, faced off true, and 
turned down to the dimensions given on the shrinkage sheet, the 
tolerance allowed being .001 of an inch only. It is inspected while 
in the lathe by an officer, who assures himself by numerous mea¬ 
surements that the shrinkage surface is of correct dimensions, and 
that no daws exist in the metal. The tube is then removed from 
the lathe and bore searched and star gauged. It is now ready for 
assembling. 

322 . The shrinking pit.— (1) The tube is placed in the shrink¬ 
ing pit breech end down. The shrinking pit is a well of square 
section having two movable tables. On the lower table, and also 

A 

ckase hoob 



on the floor of the pit, are heavy mandrels which enter the bore of 
the tube; and by screws alongside of these the tube can be made 
perfectly vertical. When pieces are to be shrunk on from the 
breech end, the tube is held vertical by four adjusting screws in 
the upper table. For small guns the lower table is moved up to 
fit the length of work. Long pieces, as 12-inch 50-caliber or 14- 
inch tubes, rest directly on the floor of the pit. To keep the tube 
cool, water is pumped in at the bottom, rising to the top and flow¬ 
ing down again through a central pipe. 

323 . Heating furnaces.—(1) A heavy collar, carrying two 
trunnions to which the chains of the crane can be hooked, is bolted 
to the jacket, and it is lowered, breech end first, into a hot-air 



















CHAPTER IX. PLATE II. 



SHRINKING ON 14-INCH Cl HOOP. 
A, Heating-Furnace (cover removed). 





312 


Naval Ordnance 


furnace. This furnace is a vertical cylinder, built in sections to 
suit the particular lengths of jackets, and is made of fire brick 
lagged with asbestos. Heat is absorbed from air which has been 
passed in pipes Over petroleum burners. Large pipes lead from 
the air heater to each end of the furnace, and also, in a furnace 
now installed, to the middle. Air is passed in at the bottom and 
out at the top of the furnace, or vice versa, as needed to maintain 
a regular rise of temperature, as shown by electric pyrometers 
at the top, bottom, and middle. Hot air is admitted at the center 
to “ boost ” the heating at the exhaust end when desired. At A, 
Plate II, is shown a furnace with the top cover removed. 

(2) For short hoops a shorter furnace is used, in which petro¬ 
leum burners play into a space between brick walls, the gases and 
flame rising around the pieces to be heated. This causes deposits 
of soot on the hoops, but the furnace is only used for hoops so 
short that they can be easily swabbed out before assembling. 

(3) In heating a gun for putting in a liner, it is difficult to get 
the required temperature in the heavy parts around the chamber; 
so an electric booster is used. This is a cylinder of fire brick, 
lagged with asbestos, and has resistance wires wound around on 
its inner surface. A 220-volt alternating current is used. A tem¬ 
perature of iooo 0 F. can be obtained with 30 kilowatts of current. 
There are two sections, each 50 inches long, which can be inserted 
in the hot-air furnace where they are most needed. 

(4) Air heating is regular, and practically no local heating or 
warping occurs. Furthermore, the jacket is kept free from dirt. 
The heating takes place gradually, a large jacket requiring 30 
hours to attain the desired temperature. Every precaution is 
taken to keep the heating uniform throughout, reversing the direc¬ 
tion of flow of the hot air when necessary. The temperatures 
used depend on the amount of shrinkage assigned, and on the 
amount of clearance necessary for assembling. In small guns, as 
little as .005 inch is sometimes considered sufficient, but in all 
14-inch work .025 inch clearance is desired, requiring the diameter 
of the hoop to be .05 inch greater than that of the part over which 
it goes. The coefficient of expansion of steel being .0000075 for 
1 0 F., the necessary temperature is easily found. 

(5) While the jacket is in the furnace, its diameter is measured 
by lowering steel cross-points into it. The lengths of these cross- 




Details of Construction of Naval Guns 313 

points are equal to the original diameter of the jacket plus the 
desired expansion. 

(6) The 14-inch jacket is given a temperature of 725 0 F. at the 
breech end and 825° at the muzzle end, so as to insure its gripping 
first at the breech end. 

324 . First assemblage.— (1) When the jacket has received the 
desired expansion, it is hoisted out of the furnace, and tried for 
diameter with cross-points, previously checked. The bore is wiped 
out with a moist muslin sponge. The jacket is swung over the tube, 
centered by men with asbestos gloves, and lowered over the tube 
until it brings up at the proper point. It is guided down by the 
workmen and turned to prevent sticking and to assist the centering. 
When it is in place, a cold spray from one of the several rings of 
perforated pipe is turned on the part which it is desired to have 
grip first—in this case the breech end. Water is in the meantime 
circulated inside the tube. When the breech end is considered 
cooled enough to grip, other sprays are turned on. at intervals of 
one minute, and then the rings of perforated pipe are hoisted 
slowly up the jacket, spraying water and cooling it, so that when 
they reach the top, the whole jacket has gripped the tube. It is 
then allowed to finish cooling gradually. Plate II shows a 14-inch 
Ci hoop being lowered over the gun in the pit. 

(2) Should the jacket “gall” or stick while being lowered, it 
is at once hoisted off and allowed to cool. The abrasions are filed 
off, and after being heated it is tried again. 

(3) The tube has already been turned to proper size to receive 
the B2 hoop, so it is left in the shrinking pit, while the B2 hoop is 
heated. When proper temperature is obtained, the B2 hoop is 
shrunk on, water being applied to make it grip at the end nearest 
the breech, as was the case for the jacket. 

(4) After the gun has cooled, it is removed from the pit. The 
jacket and hoop are measured on the marks previously scribed, to 
get their expansion in diameter, and longitudinal contraction, and 
the bore is star gauged. The internal measurements, showing 
contraction of the bore, serve as an efficient check on the shrink¬ 
age, and if the contractions do not correspond closely to those 
calculated, the question must be referred to the Bureau of Ord¬ 


nance. 


314 


Naval Ordnance 


325 . Successive assemblages.— (i) Each hoop is prepared for 
assemblage by having a rough cut taken from the outside to 
remove spring, then being bored out, bore searched and star 
gauged, after which the shrinkage sheets are made out as pre¬ 
viously described. 

(2) After the Bi and B2 hoops are assembled, the Ci hoop is 
prepared. The gun is placed in a lathe, and the outside of the Bi 
jacket and B2 hoop is turned down to the dimensions given on 
the shrinkage sheets, the gun is inspected, and placed in the 
shrinking pit. The Ci hoop is heated and shrunk on, water being 
applied to make it grip first at the breech end. When cool, the 
bore is star gauged and the compression is noted. 

(3) The Di and D2 hoops are now prepared for assembling, 
and the gun is placed in the lathe and turned down to the dimen¬ 
sions on their shrinkage sheets. The Di hoop is shrunk on, and 
as soon as the gun is cool the D2 hoop is assembled. All these 
hoops go on over the muzzle end, and all are made to grip first at 
the end toward the breech. 

(4) The D3 and C3 hoops being locking hoops, a different pro¬ 
cedure must be followed in putting them on, as is seen from an 
inspection of the drawing. This procedure is as follows: The 
hoop D3 is rough turned and bored out to the finish dimensions. 
The shrinkage sheet is made out for the C2 hoop, and it is turned 
down. Then the C2 hoop is placed in the shrinking pit, end 
toward the breech up; the D3 hoop is heated in the short furnace, 
using the direct flame and gases of the oil burners, and is shrunk 
on. Great care must be taken in this operation to have the D3 
hoop in exactly the right position on the C2 hoop, because if the 
shoulder on D3 did not enter accurately in the recess in C2, it 
would grip some of the metal too hard, crushing it, while other 
places would not be gripped at all. The assembled C2 and D3 
hoops are star gauged to note compression, when cool, and are 
then placed in a lathe, and bored out to finish inside diameters. 
The shrinkage sheet is made out, and the partially assembled gun 
is placed in a lathe and turned down to receive the two hoops. 
They are then heated together, and shrunk on the gun, the same 
care being used to make the D3 hoop grip in the proper place on 
Ci. In a similar manner, C3 is assembled on B3, and the two are 
assembled on the gun. After the final assemblage, the bore of the 


Details of Construction of Naval Guns 


3i5 


gun is star gauged and the compression caused by assembling Di, 
D2, D3, C2, C3, and B3 is noted and checked up. 

(5) The assemblage of the gun is now complete, and it is ready 
for the finish machining, rifling, etc. 

Finishing the Gun. 

326 . (1) The assembled gun is now put in a lathe, muzzle end 
to the face plate, whose jaws grip on the extra metal purposely left 
for the bell muzzle. It is carefully centered, especially with regard 
to the bore, and then tested with the balance rod for spring. The 
centers are thrown to compensate for any spring or warping, and 
then the outside is turned down to within .02 inch of finished 
diameter. The balance rod is used as necessary to see that the 
spring is completely removed. 

(2) The bore is now brought down to the finish diameters, two 
cuts with packed bits being required. The first cut brings the bore 
to .1 inch of finished diameter, the second to exact size. Great 
care is required in this operation to get the bore exactly true, and 
as close as possible to the finish dimensions. 

(3) All finish boring for new guns is done from the breech end, 
so that if the bit runs out slightly in the final cut, the center of the 
muzzle may be thrown slightly and the muzzle turned concentric 
with the bore. In relined guns, the finish boring is done from the 
muzzle end. 

327 . Chambering.— (1) While the gun is in the lathe for bor¬ 
ing, the chamber is bored out with a packed bit, and the compres¬ 
sion slope is cut with a packed bit of the proper taper. This com¬ 
pletes the chambering for guns with chambers whose diameters 
are the same from entrance to compression slope, as is the case 
in the 14-inch, and they are ready for rifling. Guns with narrow- 
neck chambers may also be rifled at this stage if desired, the 
chamber having been bored out to the diameter of the neck, or 
they may be sent to the chambering machine, where the chamber 
is finished by a special chambering bar. ThSs has a bearing in the 
bore just forward of the chamber, and the tool is fed along by 
gearing working inside the bar. To obtain the proper slopes the 
tool is fed in and out by a lug working in a slot in a key which 
extends along the bar. 


316 


Naval Ordnance 


(2) In guns using cartridge cases, the chamber is cut to the 
required form by packed bits, the finishing bit carrying a long tool 
set to the correct taper. The chamber is inspected by fitting in it 
a dummy case of the exact form desired. 

328 . Bore searching and star gauging.— (1) The gun is now 
carefully bore searched for any defects that may have appeared in 
finish boring or chambering, or for any rough spots or tool 
marks, etc. 

(2) The bore and chamber are then star gauged at each inch of 
length, except that the slope of the chamber is not star gauged, as 
a slight error in the position of the gauge would make a large 
difference in the reading, and the record would have no value. 

329 . Rifling.— (1) The rifling , which consists of cutting spiral 
grooves in the surface of the bore from the compression slope to 



the muzzle, is done, as noted, either before or after the final 
chambering. 

(2) Before rifling a gun of a new type, it is necessary to con¬ 
struct a rifling plate, and from it a rifling bar. The following 
is the procedure: A drawing is made of the curve of rifling in the 
bore developed on a plane surface, and an iron template is con¬ 
structed with one edge straight, while the other is cut to the 
developed curve of the rifling. For uniform twist, this is a straight 
line at a constant angle to the straight side, but for increasing twist 
it is a curve. This plate is secured to one side of the lathe used 
for cutting rifling bars, and has pressed against its curved side a 
roller carried in an arm extending across the bed plate. The top 
of this arm is a rack which, through a series of pinions, drives the 











CHAPTER IX. PLATE III 




& 


F IG . 2.—Lapping-Heads, 



Naval Ordnance 


3iS 

head carrying the rifling bar. As the rifling bar is fed along, it is 
turned the necessary amount, so that the rigidly held tool against 
which it is fed makes on its surface a curve like that desired in the 
rifling. A heavy weight sliding between two uprights on the car¬ 
riage, suspended from a strap wound round a wheel on the head, 
serves to keep the roller always tightly pressed against the edge of 
the template. 

The slot cut in the surface of the rifling bar is about .5 inch 
wide and .5 inch deep. To cut grooves wider at the breech end 
than at the muzzle, as is done with practically all guns, a secondary 
slot must be cut in the rifling bar, in the same manner. This is like 
the first, but differs from it enough to widen the grooves the 
necessary amount. 

(3) All rifling is done from the muzzle end. To cut the^ 
grooves, the rifling head is keyed in the socket in the end of the 
rifling bar, and carefully centered with the gun. This head (Fig. 
1, Plate III) is a hollow steel cylinder, slightly smaller than the 
bore of the gun, holding eight cutting tools arranged in pairs 90° 
apart. 

By means of wedges controlled by screws on the front face of 
the cylinder, the tools can be set out separately, or together, a 
graduated collar surrounding the central, screw giving a means of 
reading the amount when all are moved together. For large guns 
the rifling head is capable of rotation on its shaft. While grooves 
are being cut, it is held rigidly in position on the rifling bar by pins 
engaging in holes in a ring on its after end, but when one set of 
grooves is finished the pins are withdrawn and the head moved to 
the position for a new cut. For small guns, the rifling head can¬ 
not be turned on its shaft, but the gun itself is mounted in a 
graduated collar which is turned as necessary, a pointer attached 
to the lathe serving to indicate the amount of movement. 

The head being mounted, and the tools set for the first cut, the 
rifling bar is fed into the gun. A lug on its forward steady-rest 
engages in the slot cut on the bar, revolving the bar as it is fed 
forward and causing the head to cut spiral grooves of the desired 
curvature in the bore of the gun. Very small cuts are taken, to 
keep the metal from jamming in front of the tools, so that from 
15 to 30 cuts are necessary for one set of grooves. After all 
grooves have been cut, the lug on the steady-rest is engaged in the 


Details of Construction of Naval Guns 


3 J 9 


secondary slot in the rifling bar, and the work is gone over, giving 
each groove the required enlargement toward the breech. 

The cutters are kept well lubricated with oil fed in the breech 
during the entire operation. A semi-circular brass sleeve is pushed 
into the bore, by proper mechanism, at half the speed of the head, 
and helps support the shaft. 

(4) After rifling, the lands are star gauged at every inch of 
length, and the grooves, for the first eight calibers from the origin 
of rifling, are star gauged at every half-inch of length. 

330 . During the World War a number of rifling heads were 
developed, operating on the principle of a broach. These are pro¬ 
vided with a series of hardened steel disks, with cutters all around 
the periphery capable of taking a cut from 0.001 to 0.002 inch 
deep. Each disk in the series cuts from 0.001'to 0.002 inch deeper 
than the disk just preceding it, so that by using the whole series the 
rifling grooves can be cut to the required depth. When a gun is 
to be rifled, the first disk or broach in the series is secured to the 
forward end of the rifling head. The rifling bar is then fed into 
the sun from the muzzle end, the broach cutting grooves 0.002 
inch deep all around the inside of the bore. At the breech end 
of the gun the broach is removed and the rifling head drawn back 
through the gun to the muzzle. There another disk is attached to 
the head, this being the second broach in the series, and the opera¬ 
tion is then repeated. The second cut serves to deepen by 0.002 
inch the grooves cut by the first broach, and so on until the whole 
series has been used and the rifling grooves are of the proper 
depth. For guns of intermediate caliber and below, sufficient 
cutters are provided on the periphery of the broach to cut all 
grooves at one time. In the case of major caliber guns there are 
usually cutters enough for one-half the grooves. Thus a 16-inch 
gun has 96 grooves, while the broach used in rifling it is provided 
with 48 cutters. The operation of rifling the gun consists, there¬ 
fore, of two parts, but it is still much quicker than can be accom¬ 
plished with the older style of rifling head. 

331 . Finish turning—After rifling, if the gun has been cham¬ 
bered, it is returned to the lathe, where the outside is turned down 
to finished diameters, the bell muzzle is finished, and the gun is 
faced off to the correct length. In guns which are hooped to the 
muzzle, the tube projects about .25 inch beyond the end of the 


320 


Naval Ordnance 


hoop. During the turning, any opening of outside joints is closed 
by “ rolling ”— i. e., forcing a tool carrying a small wheel against 
it as the gun is revolved. 

332 . Determination of droop.—In order that the gun, when 
finally mounted, may be in the most advantageous position, it is 
now tested to ascertain the point of least droop. It is centered in 
a lathe, the breech end is gripped by the jaws of the face plate, 
and the point where the gun will be supported by the trunnions is 
held by steady-rests. The gun is now revolved, and by means of 
a small spring indicator held against the muzzle, the points of 
greatest and least comparative droop are determined. These are 
marked, and then the absolute droop at these two points and two 
other points diametrically opposite is measured, using the tail 
stock of the lathe ’for reference. From the information thus 
obtained, the position of the gun in which it shows least droop is 
noted, and the top of the breech is marked to show where to start 
the thread for the screw-box collar. 

333 . Chasing thread for screw-box collar.— (i) In all guns 
from 4 to 14 inches, inclusive, the screw-box threads are cut in a 
separate collar which screws into the breech of the gun—in some 
cases into threads cut in the jacket; in others, as the 14-inch, into 
threads cut in the Ci and Di hoops. 

(2) The gun is put in the lathe with muzzle end to the face 
plate, and the after ends of the A tube and Bi jacket are faced off 
true as one surface, both extending the same distance to the rear. 
The Ci hoop is then faced off at an exact distance in rear of the 
end of the A tube and Bi jacket, determined by an accurate gauge. 
Finally, the Di hoop is faced off at an accurately gauged distance 
in rear of the end of the Ci hoop. 

(3) The Ci and Di hoops are then bored out to exact diam¬ 
eters, using a tool mounted on a head and fed in by its carriage 
while the work revolves. These diameters having been checked 
up by steel points, a slot the depth of the thread to be chased, 
usually .25 inch, is cut in Di where it joins Ci, and in the Ci hoop 
where it joins Bi, to allow clearance for-the tool which is to chase 
the thread. 

(4) The thread is then chased, starting it at the point deter¬ 
mined by the droop measurements, so that when the screw-box 
collar is screwed home the right part of the gun will be up. 


Details of Construction 1 of Naval Guns 321 

The thread in the Di hoop is first chased, and then that in Cl, 
the latter being an exact continuation of the former. The thread 
is tested for accuracy with gauges, which must fit the threads in 
both Ci and Di hoops at the same time. 

( 5 ) The screw-box collar, prepared as noted in the manufac¬ 
ture of breech mechanisms, is fitted to the gun while it is still in 
the lathe, so that any further work necessary for fitting may be 
done at once. This work must be very accurate, as the collar must 
take up firmly against both the ends of the tube and jacket, and 
the Di hoop at the same time. In the fit with the end of the Ci 
hoop, .001 or .002 inch clearance is tolerated. 

(6) The breech is now marked for holes for heavy countersunk 
screws to keep the collar from turning, and these are drilled and 
threaded. The screws are put in place and the collar is secured. 

334 . Lapping.— (1) The bore of the gun is now lapped to 
remove all burrs, etc. First a head ( A , Fig. 2, Plate III) holding 
four segments of wood covered with emery cloth, held out against 
the bore by spiral springs, is run through, while emery flour and 
water are put in with a swab. This smooths the lands. For the 
grooves a similar head is used, but with segments of lead cut to fit 
the grooves (B, Fig. 2, Plate III). Finally, a head covered with 
burlap and waste is run through to clean out the bore thoroughly 
{C, Fig- 2 , Plate III). Clean waste is put on this head and tied 
in place with twine, as required. The heads are drawn back and 
forth through the gun by a machine which reverses itself at the 
end of the travel each way. 

(2) Though not connected with the subject of gun construction, 
it is well to mention here the question of lapping guns aboard ship. 
Quite frequently the bores of guns in service become constricted 
to such an extent that a bore plug gauge of the same diameter as 
the projectiles to be fired cannot be pulled through the guns. 
Ordinarily this constriction is due to an accumulation of copper 
from the shell rotating bands, and as such is not considered espe¬ 
cially harmful or dangerous to the gun. As will be seen later, 
however, under the subject of relining guns, this constriction is 
sometimes caused by a shoulder on the liner over-riding the cor¬ 
responding shoulder on the tube, in which case the bore of the gun 
is actually contracted to a diameter less than that of the shell, 
making it dangerous to fire the gun. In this case it becomes 
necessary to remove the obstruction to the passage of the bore 


22 


322 


Naval Ordnance 


gauge by lapping the tops of the lands. For this purpose it was 
customary for ships to construct their own lapping heads, usually 
of blocks of wood set outward by springs against the bore of the 
gun, the whole head being then covered with emery cloth similar 
to A, Fig. 2, Plate III. A line was attached to each end of the 
lapping head and drawn back and forth by members of the guns 
crew. Care had to be taken not to draw the lapping head beyond 
the actual limits of the constriction, as shown by measurement 
of the points where the bore gauge stuck, in order to avoid un¬ 
necessary wear on the gun. Such lapping heads were more or 
less crude in construction, and when possible the work was done 
at navy yards. The latter are now provided with the necessary 
equipment and measures are being taken also to supply lapping 
heads afloat. 

335 . Fitting breech mechanism.—The necessary holes for 
fitting the breech mechanism are drilled, the hinge plate or hinge 
bolt is put in place, and the breech block is fitted. Previously to 
fitting the breech block, it is fitted in a dummy gun, so that when 
actual fitting takes place the work will not be so difficult. There is 
always considerable hand work in fitting every breech mechanism. 
When the fitting is complete, the block is marked with the number 
of the gun. 

336 . Milling keyway.—Whenever convenient during the final 
finishing work on the gun, the keyway on its top, to take the key 
which keeps the gun from turning in its slide, is cut. A special 
portable milling machine operated by an electric motor is strapped 
on top the gun for this purpose. 

Note. —The processes of finishing, from rifling on, are not carried out 
in any regular order; the gun is routed through the shops as the machines 
are ready to receive it, the only requirement being that it must be finish- 
bored, finish-turned on the outside, and measured for droop before the 
threads for the screw-box collar are chased. In some cases the breech- 
mechanism has been fitted before the gun was rifled, while in others the 
rifling has been done before the final chambering. 

337 . Putting on yoke.—The yoke, of forged or cast steel, may 
be put on in several ways. In the smaller guns it is often screwed 
or shrunk on, but in most large caliber guns, including the 14-inch, 
it is put on over the breech and abuts against a shoulder on the 
Di hoop which prevents its forward movement. Just in rear of 
the yoke an annular slot is turned in the gun, in which two sections, 


Details of Construction of Naval Guns 


3 2 3 


each about 60 , of a steel ring are secured by countersunk screws, 
one at the top and one at the bottom of the gun, to prevent back¬ 
ward movement of the yoke. This annular slot for the backing 
ring is cut whenever convenient during the finishing processes of 
the gun. The yoke is now considered part of the gun. 

338 . Balancing for center of gravity.—The gun with breech 
mechanism, with a projectile and charge, is balanced on knife 
edges to find the center of gravity. This is done for only one gun 
of a type. The center of gravity of each gun is previously com¬ 
puted, in addition, for convenience in designing. 

339 . "Weight.— I he gun, with breech mechanism, is now 
weighed, and this weight is marked on the face of the breech. 
The weight of the breech mechanism is also marked on the block, 
but this is included in the weight of the gun. 

340 . Final inspection and marking.—T he gun is now finally 
inspected, the dimensions are verified, the breech mechanism is 
tested, etc., after which the gun is marked according to the stand¬ 
ard marking, which gives place of manufacture, year, mark, num¬ 
ber, and weight of the gun, and initials of superintendent and 
inspecting officer. 

The gun is then fitted to the slide and as much of its mount as 
may be necessary, and is sent to the Naval Proving Ground for 
proof firing. After it has been proved, it is returned to the gun 
factory and, if satisfactory on proof, is relapped, bore searched, 
star gauged, and issued to the service. If unsatisfactory on proof, 
the defects noted are remedied if possible, and the gun is returned 
for re-proof. 

Re-lining. 

341 . When a gun has fired a considerable number of rounds, 
the actual number depending on the caliber of the gun and its 
designed muzzle velocity, the bore becomes eroded to such an 
extent that the gun gives undue dispersion. It then becomes 
necessary to bore out the gun, insert a liner, and then rifle and 
chamber the liner. Until recently cylindrical liners were used, 
but now conical liners, tapering toward the muzzle end, are in¬ 
serted. It has also become customary, since the introduction of 
conical liners, to build guns of 5-inch caliber and above with a 
liner already inserted. When it becomes necessary to re-line, the 


3 2 4 


Naval Ordnance 


original liner is simply pulled out from the breech end of the gun 
and a new one put in its place. 

The operation of lining a gun consists in the main of preparing 
the gun to receive the liner, machining and shrinking in the liner, 
and finishing the gun. If the gun has previously been unlined, it 
is necessary to bore out the tube sufficiently to receive the liner. 
This is done by placing the gun in the lathe and roughing out the 
bore with packed bits, followed by a final boring with a number 
of tapered bits. All boring is done from the breech, and the taper 
is .003 inch to the inch, the diameter decreasing from breech to 
muzzle. 

The rough boring is done similarly to that described in para¬ 
graph 314. The cuts are made successively from the breech, and 
there are one, two, or three shoulders, so that, as far as possible, 
the amount of metal to be removed by the tapered bits may be 
reduced. The latest practice is to confine the number of shoulders 
to one or possibly two, located well back near the origin of rifling. 
It was found that, with shoulders out toward the muzzle, the 
mandrelling effect of the projectile passing down the bore was 
liable to cause the relatively thin-walled liner to “ ride up ” on the 
shoulders on the tube, thereby producing a constriction in the bore 
of the gun. 

After roughing out with packed bits, the bore is smooth bored 
with tapered bits. The bit for the muzzle section is first run 
through to the muzzle. Then the next bit in rear is run through 
to within a few inches of the beginning o'f the cut made by the 
muzzle bit, and then this bit is withdrawn, the two cuts are star 
gauged, and the bit is replaced and worked carefully up to the 
line between the two cuts, taking care that no shoulder or ridge is 
left. This merging of the one cut into the other is known as 
“ blending ”; the forward end of each bit is made with the diam¬ 
eter for several inches coincident with that of the last few inches 
of the previous bit, so that the “ blend ” may be made smooth by 
overlapping the cuts. The several bits are put on in turn, each cut 
being blended into the previous one, until the entire length of the 
gun is bored. The feed is very slow, about 6 to 7 inches an hour. 

After the boring is completed, the bore is star gauged through¬ 
out its length, and a shrinkage sheet for the liner is made out. 
The shrinkage is very small, only from .005 to .006 inch for 
12-inch guns, and less for smaller. This shrinkage is enough to 


Details of Construction of Naval Guns 


325 


hold the liner in place, without undue strain thereon, since, in the 
calculations of the gun, the liner is not considered as an additional 
layer for giving elastic strength by shrinkage. The liner is rough 
turned from the forging, bored out to within .65 inch of its final 
diameter, and then replaced in the lathe for turning. With the 
shrinkage sheet prepared for it, it is finish-turned, using a head 
which feeds the tool slowly along, and is then smoothed down by 
filing any rough spots. It is then coated with a mixture of graphite 
and machine oil. (It may be left dry, but this coating prevents 
“ galling ” in shrinking.) 

The gun is placed, muzzle down, in the furnace, and is heated 
thoroughly to a temperature of 400° to 500° F. A brass plug is 
then screwed into threads cut in the muzzle of the liner (to keep 
the hot air in the gun from getting inside and expanding the liner 
as it is inserted), and a steel lifting plug is screwed into the breech. 
Into this lifting plug are shackled the crane falls. A rope sling is 
placed about the muzzle end of the liner and the whole is hoisted, 
the liner in a horizontal position, and then the sling is slacked 
until the liner is hanging vertically, when the sling is removed. 
The crane is then moved until the liner is hanging directly over 
the gun. The heat is turned ofif and the lid of the furnace is 
removed. The vertical position of the liner is verified by a spirit 
level, and its position over the center of the gun is tested by plac¬ 
ing a wooden batten against the liner at four quadrantal points, 
and noting the position, on the breech of the gun, of a pointer 
attached to the batten. 

The liner is slowly lowered until its muzzle is within the breech 
of the gun. It is then lowered rapidly, checking as it is about to 
pass each shoulder, until in place. The crane falls are unhooked, 
and a heavy iron head is put over the liner, a hydraulic jack is 
placed above this, and over all a heavy yoke which takes under 
nuts on the tops of two heavy tie-rods passing down through the 
sides of the furnace. Pressure is put on the jack, and the liner is 
held firmly in the gun, preventing its backing out on cooling. The 
gun is then allowed to cool, no water being sprayed on, but one 
section of the furnace being removed to allow free access of air. 
After four or five hours, or when it is considered that the liner 
has “ set,” the jack is removed, and the lifting block is unscrewed 
and removed. 





326 


Naval Ordnance 


After the gun is thoroughly cooled it is removed, and then cham¬ 
bered, rifled, and finished as described above. 

In fitting a cylindrical liner the process is similar, but, after the 
rough boring, smooth boring is done by straight packed bits 
instead of the tapered bits, and one bit is sufficient for each section 
between shoulders. The cylindrical liners are generally thicker 
than the tapered, and the shrinkages greater. 

342 . Some guns have been built with liners in them originally, 
as is the case of the 12-inch, Mark VII. These liners are cylin¬ 
drical, and fit smoothly, without shrinkage, inside the tube. The 
processes of boring and turning the tube and liner are similar, 
respectively, to those of fitting a cylindrical liner to an old gun. In 
assembling, the tube is heated to 500°, and lowered over the liner. 
On cooling, it makes a snug fit with the liner, and the gun is then 
assembled complete on the lined tube, as above described. The 
great objection to cylindrical liners is that they may not be readily 
removed when they are worn out, but must be bored out, thus 
slowly cutting away all the metal of the liner, with great loss of 
time and labor. The replacement of conical liners, however, is 
very simple. The gun is placed in the shrinking pit and heated 
to about 500° F. The cold water is turned through the liner. As 
the liner cools, it contracts, and may be allowed to fall out (gun 
being in the pit with muzzle up, and blocked several inches off the 
bottom) or may be pulled out by the crane (gun being breech up). 

Gun Construction by Radial Expansion. 

343 . In the method of gun construction just described, the 
necessary tangential strength is obtained by shrinking one or more 
hoops over the tube, thus placing the metal in a condition of 
initial strain. 

Another method is now being employed to a certain extent by 
the navy, known as the “ Radial Expansion Method of Gun Con¬ 
struction.” 

The basis of this method of gun construction is the application 
of hydraulic or other pressure to the interior of the gun tube, by 
which the metal of the gun is cold stretched beyond its elastic 
limit, acquiring a permanent set. Metal which has thus been 
stretched acquires a new elastic limit greater than the original 
elastic strength of the metal, depending upon the amount of perma¬ 
nent elongation. 


Details of Construction of Naval Guns 


327 


344 . It has been known for more than 50 years that when a piece 
of steel is stretched beyond its elastic limit, thus acquiring a perma¬ 
nent stretch, there is imparted to it at the same time a new elastic 
limit greater than the original elastic limit of the metal, depending 
on the amount of permanent elongation produced. 

Numerous and extensive experimentations have been carried 
cut to ascertain the laws of this “ Special Elasticity,” and one of 
the results established is that the special elasticity, by gradual 
stretching in the above way, may be increased so as to practically 
coincide with the ultimate strength of the metal. 

345 . Along with these experiments were conducted others for 
determining the effect of cold stretching of hollow cylinders by 
the application of internal pressure. It has been only within the 
last 20 years or more that this process has been applied to steel, 
although certain experiments performed in 1874 established the 
fact that the elastic limit of steel obeyed the same general laws as 
earlier metals experimented with, and this process could be applied 
with great advantage to the hooping of built-up guns. 

346 . The convincing part of the process is that upon gradual 
application of internal hydraulic pressure the metal of the walls of 
the gun begin to “ flow ” upon reaching a pressure of from 36,000 
to 60,000 pounds, the theoretical elastic strength of the gun, de¬ 
pending on the metal. 

For instance, a nickel-steel tube which was shown on test to 
have an elastic limit of 60,000 pounds per square inch was sub¬ 
jected to hydraulic pressure on the interior amounting to 107,000 
pounds per square inch. The external diameters of the gun con¬ 
tinually expanding indicated a continuous flow of the metal beyond 
the elastic limit. At this point the pressure was released, and the 
exterior diameters returned toward their original value to a point 
which gave the permanent set of the metal. The permanent in¬ 
crease in the interior diameter was about 6 per cent to 8 per cent. 
After a mild heat treatment the new elastic limit of the material 
was determined to be approximately 110,000 pounds per square 
inch. 

347 . Whatever theory there may be concerning this method of 
gun construction, there is no doubt whatever that the elastic 
strength of the gun under experimentation had been raised from 
60,000 to about 110,000 pounds per square inch, an increase of 


328 


Naval Ordnance 


80 per cent over its original value, showing the remarkable effect 
of the process on the elastic limit of the metal thus treated. 

348 . A further remarkable feature connected with this process 
is the condition of the initial strains in the metal walls of the tube 
as a result of cold stretching. Specimen rings cut from the waste 
metal at muzzle and breech show that the theoretical state of initial 
strains, shown by the theory of the process, exist in fact. The 
outer ring shows an initial strain of tension, while the inner ring 
shows a state of compression, the intervening hoops showing a 
gradual change through a neutral axis between these two ex¬ 
tremes, which is the ideal condition for the walls of a gun. It is a 
condition, or an effect which the French have designated “ auto - 
frettage ” literally “ auto-hooping.” The method of treatment 
they call “ ecrouissage,” meaning “ hard hammered.” It accom¬ 
plishes, with more uniform results, the same effect produced by 
shrinking hoops on a built-up gun. 

349 . It has thus been practically and most thoroughly demon¬ 
strated that if a homogeneous metal tube is submitted to pro¬ 
gressively increasing interior pressures its different concentric 
layers will take on successively permanent deformations, starting 
from the innermost layer. The layers thus deformed under 
pressure will remain in a deformed state after the removal of the 
load; in preventing the return of the outer layers to their original 
position the inner layers remain strained when they themselves, 
due to reaction, are contracted. The tube itself has acquired, in 
being deformed, the ideal composition of uniform auto-hooping, 
in which all the layers are equally affected as regards resistance. 

In other words, the gun is made in one piece, or as it is called 
of “ monoblock construction.” 

350 . From a theoretical standpoint, there is no reason why this 
process may not be extended to the construction of the 16-inch 
50-caliber gun, with all the advantages which it has shown for 
guns which may be constructed in a single piece. The mere ques¬ 
tion of size ought not to be a deterrent for the application of the 
process to these larger caliber guns. The formulas clearly indi¬ 
cate that it is not a question of size of diameter, but merely a ratio 
of external and internal diameters. 

351 . For the manufacture of guns by the radial expansion 
method the special equipment necessary consists of a pump, an 
“ intensifier,” a system of piping capable of withstanding high 


Details of Construction of Naval Guns 


329 


pressures, and a suitable means for closing the ends of the forging 
that is to be stretched. The gun forging, bored out to a diameter 
somewhat less than the finished size desired, is successively 
stressed beyond its elastic limit, and careful measurements taken 
to ascertain the deformation produced. A mild heat treatment 
follows, which has the effect of “ ageing ” the metal and making 
permanent the increased elastic strength acquired by the stretch¬ 
ing. The forging is then ready for finish boring, turning, and 
rifling as already described for built-up guns. 

352 . The advantages of this method are: 

(a) Much lighter gun as compared with a gun of the same 
caliber produced by the old method. 

(b) Less machine work, because of fewer surfaces to bore and 

turn. 

(c) Less labor required in manufacture. (Less number of 
forgings to make and transport.) 

(d) Cheaper and quicker gun construction, and hence increased 
output. 

353 . The only limiting feature of this method of gun construc¬ 
tion appears to be the thickness of gun forging that can be de¬ 
pended upon as sound and free from defects. 

354 . So far only guns of intermediate caliber have been made 
by the radial expansion method. A 4-inch gun constructed by 
this process has been fired up to 464 rounds, and the life of the 
gun has not been reached. The velocity has been reduced by 100 
foot-seconds, and the bore shows some wear, and slight increase 
in diameter. This gun was fired in comparison with the navy 
standard 4-inch gun, and has shown itself the equal of the standard 
gun in every way. 

Inspections—Gun Structure. 

355 . The inspections pursued in the course of the manufacture 
and assemblage of the gun itself—disregarding the breech 
mechanism—have been noted as they occur in the progress of the 
work. They may be summarized, for reference, as follows: 

(1) Inspections by officers.—The inspection officer in charge 
of major caliber guns is in general responsible for all work on 
the guns, and his initials are stamped on the breech of each gun. 
His duties, aside from general supervision, are: 


330 


Naval Ordnance 


(a) The bore searching of all forgings after rough boring, and 
the checking up of marks put on them by the steel works. 

(b) All bore searching of finished or unfinished pieces, when¬ 
ever noted in the description of manufacture. The officer also 
signs the statement in the star-gauge record book, giving date of 
inspection and any defects found. 

(c) The. checking up of the measurements marked on each 
shrinkage sheet with the star-gauge readings, and the checking 
of the measurement of the external diameter of the male part, 
when the finish turning is completed, to see that it conforms to 
the shrinkage sheet. 

(2) Inspections by workmen.—During the progress of the 
work, measurements are taken by the workmen as often as neces¬ 
sary to insure accuracy. For all work, except turning conical 
liners, the men are furnished with steel points of the exact length 
of the desired diameters. These points are prepared in the tool 
shop, and are checked up on the special measuring machine in 
the gun-shop office. They are either used directly for measuring 
or are used in setting snap or beam calipers. For conical liners, 
the diameters are taken with snap calipers fitted with micrometer 
gauges. These gauges, as received from the manufacturer, are 
calibrated on points previously checked by the measuring machine, 
so that all measurements refer to this machine. 

All internal diameters are measured by the star gauge, as noted. 
The rings for setting this gauge are checked by points calibrated 
on the measuring machine. 

All fillets, screw threads, and curves, such as the bell muzzle, 
are tested during turning by profile gauges, made in the tool shop 
and issued to the workmen. 

To measure the distances between surfaces, such as the rear 
faces of the tube and hoops, right-angled gauges which bear on 
one surface and have a leg which should just extend to the other 
are used. The clearance between this leg and the surface it should 
touch is tested in accurate work with feelers or cigarette papers. 
If the paper can just be pulled out without tearing, the clearance 
is .001 inch; while if it is held firmly, the clearance is not more 
than half that amount. 

As each job is finished by the workman it is inspected by a 
responsible leading man or quarterman, using the appropriate 
gauges and steel points 


CHAPTER X. 

NAVAL GUN MOUNTS. 

Nomenclature of Gun Mounts. 

356 . The mount.—The entire system interposed between the 
gun and the structure of the ship which serves to support the gun, 
secures it to the ship’s structure, and provides for its elevation, 
train, recoil, and counter-recoil, is known as the mount. 

k 

357 . The mount consists of the following parts: (i) stand, 
(2) carriage, and (3) slide. 

The parts are defined as follows : (See Plates J and II.) 

(1) The stand is that part of the mount which is secured to 
the structure of the ship, and in or upon which the carriage rests 
and is moved in train. 

(2) The carriage is that part of the mount, supported by the 
stand, and which in turn supports the slide. To it are secured the 
trunnion seats, and in the case of pedestal mounts, the elevating 
and training gear. 

(3) The slide is that part of the mount that supports the gun. 
The slide forms the sleeve through which the gun moves in recoil. 
The trunnions are secured to it and form an integral part. 

Note. —Stands may be “ pivot-stands,” “ cage stands,” “ rail sockets,” 
“ port-sill sockets,” “ boat stands,” “ pillar stands,” “ field-carriages,” or 
any of numerous other special types. 

358 . Type names, such as “ turret,” “ pedestal,” “ port sill,” 
“ military top,” “ rail,” “ boat,” “ field,” etc., are sufficiently 
descriptive of a mount, and the names of the several parts may be 
used without modifying words. 

The term pedestal mount is self-explanatory. The 3-inch, 4- 
inch, 5-inch, 6-inch mounts, and smaller mounts, are of this type. 

Definitions—Discussion. 

359 . The principal requirements of a modern gun mount are: 
(1) Safety under all conditions, which necessitates proper design 
and requisite strength of materials, so that the mount will perform 
its function with the least danger to the personnel operating it; 


33 i 


332 


Naval Ordnance 


(2) rapidity, ease, and smoothness of operation; (3) facility of 
adjustment; (4) simplicity and reliability; (5) gradual absorp¬ 
tion of the shock of recoil and its dispersion over a sufficient area 
of the ship to prevent injury to the ship’s structure; (6) accurate 
and reliable control of power, either hand or motor power. 

360 . All modern naval gun mountings are now designed to 
have an arc of elevation as follows: Turret guns, 40° elevation, 
5° depression; broadside guns, 20° elevation, io° depression. 
The train is usually limited only by the ship’s structure and the 
location of the mount in the ship. 

361 . Mounts are conveniently divided into classes according to 
the kind of recoil mechanism used. These classes are (1) 
hydraulic-recoil spring-return mounts, (2) hydraulic-recoil spring- 
pneumatic-return mounts, (3) hydraulic-recoil pneumatic-return 
mounts, (4) hydraulic-recoil hydraulic-return mounts. In all 
recoil mounts, means are afforded for returning the gun to battery, 
i. e., its initial position; this mechanism also assists to a limited 
extent in checking the recoil of the gun. The gun recoils in the 
line of fire. In all but the smaller mounts, buffers of some form 
are provided for cushioning the counter-recoil. 

362 . A hydraulic-recoil spring-return mount is one in which 
the recoil is checked by the by-passing of the liquid contained in 
the hydraulic cylinders from one side of the piston to the other 
during recoil, and the gun is returned to its battery position by 
springs. 

363 . A hydraulic-recoil spring-pneumatic-return mount is 

one in which the recoil is checked by the by-passing of the liquid 
contained in the hydraulic cylinders from one side of the piston 
to the other during recoil, and the gun is returned to its battery 
position by combined action of springs and compressed air. 

Note.— This type of recoil mechanism was adopted when the elevation 
of the turret guns was increased from 20° to 30°. Later, when the angle 
of elevation was increased to 40° the springs were entirely abandoned, and 
compressed air used. 

364 . A hydraulic-recoil pneumatic-return mount is one in 

which the recoil is checked by the by-passing of the liquid con¬ 
tained in the hydraulic cylinders from one side of the piston to 
the other during recoil, and the gun is returned to its battery posi¬ 
tion by compressed air. 


Naval Gun Mounts 


333 


365 . A hydraulic-recoil hydraulic-return mount is one in 

which the recoil is checked by the by-passing of the liquid con¬ 
tained in the hydraulic cylinders from one side of the piston to the 
other during recoil, and the gun is returned to its battery position 
by hydraulic pressure. This type of recoil mechanism has been 
consistently adhered to by the British Navy for their turrets. 
There are none of these mounts on vessels now in commission in 
tfie U. S. Navy. 

366 . A field mount, as used in the U. S. Navy, is one intended 
for shore use, and consists essentially of an axle mounted on two 
wheels, bearing a trail piece with a small trail wheel and a socket, 
to which is secured the gun mount proper. Except for machine 
guns, which have non-recoil mounts, hydraulic-recoil spring-re¬ 
turn mounts are used. Train is effected mainly by swinging the 
whole mount on its wheels. In addition to the train thus pro¬ 
vided, a limited amount of train of the carriage on the trail is 
provided on recent mounts. The elevating gear is fitted to the 
non-recoiling part of the mount. The general navy method is to 
carry ammuntion on the gun mount, as a ‘ limber hooped to the 
trail of the mount is too heavy to be dragged by men. 

367 . A turret mount is one in which heavy guns are mounted 
in an armored structure, which is revolved on rollers by suitable 
machinery, the guns being elevated independently of the structure. 

368 . The elevating gear, hand or power, is the machinery 
secured to the carriage which elevates or depresses the gun. The 
weight of the gun, powder charge, projectile, and other parts 
supported by the trunnions, are balanced at the trunnions. On 
firing, the gun moves to the rear, thereby disturbing this balance, 
and throwing extra forces on the elevating gear. (See Plates I 

* and II.) 


Metals Used in Gun Mounts. 

369 . The metals used for naval gun mountings are cast steel, 
forged steel, and special bronzes. Cast iron is not used. Cast 
steel is used for the principle strength members, such as the 
carriage, slide and stand, and also for the larger castings of the 
elevating and training gear. Bronze is used for all bearings and 
bushings where moving parts are of steel. Bronze is also used for 
the smaller castings, where the use of cast steel is impracticable, 


I 


334 


Naval Ordnance 


on account of the difficulties of casting, and for all metal parts 
coming in contact with the powder. 

General Description. 

370 . The following is a description of a typical broadside gun 
mount: 

The slide (Fig. 2, Plate I) is a cylindrical steel casting fitted 
with a front and rear liner, in which the gun barrel slides in recoil. 
Cast solidly on the slide are two trunnion (Fig. 2, Plate I) bosses 
which support the slide and gun in the carriage. Beneath the 
slide and cast integrally with it are two circular brackets that 
support the recoil cylinders (Fig. 2, Plate I). Between the recoil 
cylinder brackets, at the forward end of the slide, is a pad to which 
is fixed the adjustable elevating arc (Fig. 3, Plate I). Recoil is 
checked by means of the combined action of the recoil cylinders 
and counter-recoil springs. Lugs are provided on the slide for 
the sight and other accessory apparatus. 

The two arms of the carriage, which support the slide trunnions, 
are cast solidly with the hollow base and terminate in seats for the 
cap squares and frictionlcss bearings. Elevation is accomplished 
through a two-hand drive mounted on the left-hand side of the 
carriage and functioning through bevel gears and a worm to the 
elevating pinion, which meshes with the elevating arc. Brackets 
are bolted to the side of the carriage to support this mechanism. 
The arc of elevation is from io° below horizontal to 20° above. 
All mounts are fitted with firing keys for electrical firing. Per¬ 
cussion firing on some mounts is accomplished by means of a hand 
lever mounted on the left-hand side of the carriage. It functions 
through a series of levers and telescopic shafts to the gear on the 
breech mechanism. A foot-firing gear is being fitted to some of 
the recent mounts. 

The gun carriage is trained by means of a two-hand mechanism 
carried on brackets on the right-hand carriage arm, operating 
through bevel gears to a worm meshing with the training circle, 
which is bolted to the stand. Platforms for the pointer and 
trainer are bolted rigidly to the base of the carriage. A bracket 
for supporting the battery box is also secured to the carriage base. 
The arms of the carriage are now made with extending shoulders 


Naval Gun Mounts 


335 


to which are bolted armored shields for the protection of the gun 
pointers. 

The stand projects into the hollow base of the carriage, where 
it is guided by upper and lower bushings bearing against the bear¬ 
ings within the carriage base. The weight of the carriage is borne 
by conical rollers, which turn on hardened steel roller paths, 
housed in the carriage base and stand. A flange projecting up¬ 
ward from the base of the stand supports the training circle and 
the indicator arc. Water-tight doors on opposite sides of the 
carriage base make the bearings readily accessible for inspection 
and give access to the holding-dozen clips. 

The sight is supported on a yoke fastened to the lugs on the 
slide. The elevation and azimuth handwheels are conveniently 
located near the sight-setter’s position on the left side of the mount 
behind the pointer. 

The pointer’s and trainer’s telescopes are yoked together so that 
the same movements for elevation and azimuth can be made to 
both telescopes by one sight setter, and thus avoid the possibility 
of having the pointer’s and trainer’s telescopes disagree in adjust¬ 
ment. By the arrangement shown, the pointer and trainer are in 
effect observing the target through one telescope. 

A voice tube, terminating in a megaphone near the sight setter, 
provides for communication between the mount and the fire- 
control station. Shoulder braces bolted to the hand-wheel bracket 
are provided for the pointer and trainer. 

Action During Recoil. 

371 . Recoil is regulated by the by-passing of the recoil liquid 
through the grooves in the cylinder liners and by the simultaneous 
compression of the springs as the piston rods are withdrawn. . At 
battery, practically all of the recoil liquid is in rear of the pistons 
since the pistons are designed to fit tightly against the forward 
cylinder heads. When the gun recoils, the energy is dissipated 
through the heat generated by the friction of the recoil liquid as it 
is forced by the piston head through the grooves in the cylinder 
liners. Pressure within each recoil cylinder during recoil is made 
approximately uniform by the design of the throttling grooves 
which vary with the stroke of the piston. Pressure between the 
two cylinders is balanced through an equalizer pipe connecting the 


336 


Naval Ordnance 


cylinders. Recoil is retarded partially by the recoil springs which 
are compressed during recoil; but the chief function of these 
springs is to provide energy to return the gun to battery. Counter¬ 
recoil momentum is dispersed as the counter-recoil plungers enter 
the counter-recoil chambers in the forward cylinder heads and 
force the recoil liquid through orifices provided. 

The Frictionless Bearings. 

372 . The upper surfaces of the carriage cheeks are machined 
to provide slots into which fit cap squares secured with cap-square 



CAP SQUARE- 

ADJUSTING SCREW 


LOCKING CLAMP 


EXTENDING LUG 


SPRING BAR 


ROLLER BEARING 


ROLLER BEARING SEAT 


CARRIAGE 


LOCKING CLAMP BOLT NUT- 

LOCDNC CLAMP BOLT- 

KNIFE EDGE- 

KNIFE EDGE BEARING- 


Fig. 62.—Details of Frictionless Trunnion Bearing. 


bolts (see Fig. 62). Lost motion resulting from wearing of the 
trunnion bushings or seats is eliminated by cap-square shoes 
fitting into slots in the cap squares. These wedge-shape shoes are 
forced into the slots by means of cap-square adjusting nuts turn¬ 
ing on cap-square studs and bearing against shoulders on the 
outer ends of the cap-square shoes. The inner ends of the cap- 
square studs are screwed into the cap squares. 

























































































CHAPTER X. PLATE I. 








Fig. i 


5//c/e. 


















































































































































































































































































































































































































































































. 
















» • 









1 



PRISMATIC SIGHT 


CHAPTER X. PLATE II. 


SIGHT YOKE 


SLIDE 


FIG. 2. 


CEP 

YOKE 


elevating gear 


TRAINING CIRCLE 


FIG. ,R. 

VIEWS OF 5-INCH MARK XIII AND MODIFIED MOUNTS. 


STAND 


4 














Naval Gun Mounts 


337 


The knife edges, upon which the oscillating parts rock when 
the gun is elevated or depressed, are housed within pockets cut 
in extending lugs on the outer ends of the trunnion bosses. Each 
knife edge slides in the lower end of the recess of the trunnion 
boss and is adjusted and secured in position by an adjlisting screzv 
which threads through the extending lug and is maintained in the 
desired position by a locking clamp secured by a locking-clamp 
bolt. 1 he dead weight of oscillating parts is transferred from the 
knife edge to a knife-edge bearing held by a drive fit in a slot in 
the upper surface of the spring bar. The spring bar is supported 
on two alloy-steel rollers. Curved recesses at each end of the 
spring bar serve as upper roller paths; similar recesses in the 
roller bearing function as lower roller paths. The roller bearing- 
rests upon a projecting shoulder cast on the carriage cheek below 
the trunnion seat. When the gun is at rest, the weight of the 
oscillating parts is carried by these frictionless bearings which 
transfer the weight directly to the carriage cheeks; but when the 
pressure on these bearings is increased by firing, the spring bars 
deflect and allow the trunnions to bear against the trunnion seats, 
removing strain from the frictionless bearings and providing 
ample support for the gun and slide. The frictionless bearings 
are protected by trunnion bearing covers bolted to the carriage 
cheeks. 

Adjustment of Frictionless Bearings. 

373 . If the gun and slide are not properly and accurately 
balanced on the trunnions the pointing mechanism will operate 
sluggishly. The cause for this generally will be found in the 
adjustment of the frictionless bearings rather than in balance of 
the gun within the slide. If the adjusting nuts are not adjusted 
so as to transfer the weight of the gun and slide to the spring bars, 
or if they are so adjusted that the trunnions are forced against 
the upper surfaces of their bearings, then the frictionless bearings 
will not function properly and elevation and depression will be 
difficult. These discrepancies may occur in either one or both 
bearings. Accurate adjustment of these bearings is easily accom¬ 
plished by turning the adjusting nuts until thin test strips of 
paper may be inserted between the trunnions and their bearing 
surfaces, after which the adjusting nuts may be locked securely 
with the locking clamps provided. 


23 


338 


Naval Ordnance 


General Discussion of Turret Mounts. 

374 . The turret installation on each class of ship varies, being 
a gradual development from type to type. For modern battle¬ 
ships the U. S. Navy has adopted the three-gun turret, four turrets 
per ship, combination as being the most efficient arrangement of 
main battery. In general, the developments in turret design have 
progressed from the use of a single gun in a turret, to a maximum 
of four guns in a turret. It may be accepted that this development 
is based upon sound principles and follows a corresponding in¬ 
crease in the size of the navies of the principal powers. 

375 . The primary objects to be accomplished in the design of a 
turret are accuracy and rapidity of gun fire, and efficiency and 
reliability of all mechanical features of the turret, combined with 
the maximum possible protection against damage by the enemy’s 
gun fire. The details of gun and mount should be worked out to 
eliminate excessive dispersion, and to avoid any increase in dis¬ 
persion, caused by any progressive permanent deflection in metal 
which is strained by the forces resulting from the discharge of the 
guns. The various machines installed for use in the service of the 
guns should be designed with a liberal factor of safety to insure 
continuous operation over an extended period of time, and should 
be simple in design to facilitate upkeep, and to avoid the necessity 
of too much mechanical skill and experience on the part of the 
personnel. Protection is similar to insurance against accident and 
should be the maximum which can be obtained without undue 
sacrifice of accuracy of gun fire and mechanical reliability. 

376 . The most important subjects that require consideration in 
connection with turret designs are: 

(a) ' Accuracy of fire. 

(b) Rate of fire. 

(c) Simplicity and reliability of machinery. 

(d) Strength and reliability of turret structure. 

(e) Size of barbettes and dead weight of turrets. 

(f) Safety features. 

377 . From the constructor's point of view, it has been prac¬ 
tically demonstrated that the weight of installation per gun is the 
least for a three-gun turret, and increases in both directions from 
this number, due to the fact that the space occupied by that por¬ 
tion of the three guns contained inside the turret pan is bounded 


Naval Gun Mounts 


339 


very nearly by a square, which is the largest rectangle which can 
be inscribed in a circle of a given size. It is also true that the least 
weight is required for designs where all guns are carried in one 
slide, but flexibility is thereby lost. 

378. The earlier turret designs in the U. S. Navy were two-gun 
turrets with what is known as a single-stage hoist. That is, the 
powder and shell were taken from the magazines and shell rooms 
and placed in a car for each gun, which was hoisted to the breech 
of the gun, traveling up and down in an open well. The guns were 
loaded, using rammers fixed in the rear of the turret, so that the 
guns had to be brought to the horizontal position to be loaded. 

379. When modern target practice was introduced in the navy, 
about 1903 , there occurred several very serious turret accidents, 
due to this open type of construction; and all turrets were modi¬ 
fied by fitting them with automatic shutters, to seal the handling 
room from the turret chamber, except at the instant the car was 
passing the shutter. This was not entirely satisfactory, and new 
designs were made on the two-stage-hoist principle; that is, the 
powder and shell were brought up from the handling room in one 
set of cars, and transferred to another set which carried them to 
the guns. This permitted the introduction of a more positive flame 
seal between the turret chamber and the magazines. Variable 
loading positions were also provided by putting the rammer on an 
arm from the gun slide, thus permitting the gun to be loaded at 
any angle of elevation, as is still the practice in the British Navy. 

380. A further change was soon made as the demands for 
rapidity and reliability of fire grew, and the turrets were nearly 
all converted to “ hand loading.” In this system the cars and 
rammers were done away with. The shell was hoisted vertically in 
a tube hoist, the powder passed up from the handling rooms by 
men standing on fixed platforms, and a wooden hand rammer was 
used. 

381. With an increase in caliber over that of 12 inches, the 
weights involved became too great and a return to power loading 
became necessary. This also led to a reduction in the number of 
men required for the turret’s crew. 

382. The designs gradually developed to that now in use ; by 
the introduction of the reciprocating shell-hoist tube, the separate 
powder car, and a chain rammer secured to the turret; thus again 


340 


Naval Ordnance 


necessitating a fixed loading position; the complications involved 
by retaining the variable loading feature not being considered 
justified. The importance of shell seating also led to the power 
rammers being re-installed in all 12 -inch turrets of dreadnoughts. 

In the latest 16 -inch turret designs the reciprocating powder 
hoist car has been replaced by a conveyor hoist similar to that used 
for broadside guns, and in all the later turrets the use of straight 
electric control has been replaced by control through universal 
speed gears, as will be seen in the detailed description following: 

14-Inch Three-Gun Turrets. 

383. The description which follows applies generally to turrets 
of vessels of the New Mexico and California classes. 

The principal parts of a turret mount are: ( 1 ) The gun, 
breech mechanism and yoke, ( 2 ) slide, including recoil and 
counter-recoil mechanism, ( 3 ) deck lugs, ( 4 ) elevating and train¬ 
ing gear, ( 5 ) shell and powder hoists, ( 6 ) rammer and spanning 
tray, ( 7 ) sights. (See Plates III and IV.) 

The turret booth is an enclosed space in a turret occupied 
habitually by the officer in command of the turret when in opera¬ 
tion. (See Plate III.) 

The turret chamber is that part of the turret surrounding the 
gun positions. It includes the gun chambers and the gun pits. It 
does not include the center girder spaces nor the wing girder 
spaces, when these are separated from it by the nature of the 
construction. 

The magazines are enclosed spaces ill which powder is stowed. 

The shell rooms are enclosed spaces in which the projectiles are 
stowed. Shell stowage is the term used to designate open spaces 
where shells are stowed. 

The handling rooms are spaces not mentioned above which are 
habitually utilized in the ammunition supply train for transferring 
powder or shell from their stowage to the supply hoists, from one 
hoist to another, or from one means of supply to another means 
of supply. These may be further distinguished as powder-hand¬ 
ling room and shell-handling rooms. 

Each turret has a turret booth separated from the turret cham¬ 
ber by flame-proof bulkheads, and so designed as to give the turret 
officer a direct view of the guns through suitable dead lights. 
Access to the turret chamber is obtained through suitable doors. 


Naval Gun Mounts 


34i 


Rach turret booth has a quick-acting lever or other device for 
operating mechanically the sprinkling system in the turret cham¬ 
ber. The turret booth is also fitted with a lever or other device 
for operating mechanically an emergency alarm. 

384. The general requirements regarding turret construction 
require that nothing shall he attached to the turret armor except 
fittings required by the structure, or which by their nature and 
use cannot otherwise be placed for the efficient operation of the 
turret. Means are provided to prevent bolts, nuts, rivet heads, 
etc., flying in the turret as the result of shell impact. In all turrets, 
except three-gun single-slide turrets, flame-proof bulkheads are 
fitted to separate the several guns from one another. 

385. A gun spray is installed near the breech of each gun and 
fitted with a quick-acting valve controlled from the turret booth 
and gun chamber. This spray is fitted on the end of a flexible hose 
capable of being used in the gun breech or any other part of the 
turret gun chamber. 

386. Each gun in the turret is fitted with a gas-expelling device, 
and blowers are installed in the turret for ventilating purposes. 
A sprinkling system is also installed to drench powder in the 
upper handling room w T here exposed in case of fire. Voice tubes, 
bells, buzzers, telephone and fire-control instruments are also 
installed as called for by the latest instructions. The usual fittings 
installed on the forward bulkhead of the turret officer’s booth are 
shown in Plate V. 

387. The intakes of the turret ventilating system are so located 
as to minimize the possibility of drawing into the system gases 
from fires in action. Care is taken, in so far as practicable, to keep 
water and spray from entering the turrets through the gun ports, 
and sighting slits, while the turrets are being operated. 

388. All machinery of a modern turret is electrically operated 
and speed is controlled through universal speed gears. 

389. The turret structure, to which the armor and all revolv¬ 
ing parts of the turret are secured, is built up of rolled-steel plates 
and angle irons, and revolves on rollers supported by a roller path 
which is secured to the structural steel foundation built into the 
hull of the ship, and included inside the barbette armor. (See 
Plates III and IV.) The rollers which are frustrums of cones, 
are spaced by a separator ring floating on the roller axles. The 
weight and vertical forces resulting from firing, are supported by 


342 


Naval Ordnance 


the conical surface of the roller, and the horizontal thrust due to 
firing, is transmitted from the revolving structure to the turret 
foundation through the roller flanges. The turret is also pro¬ 
vided with holding-down clips (see Plate III) to prevent it from 
being thrown from its foundation by force from any outside 
source. The circular barbette armor extends from a point just 
below the armor secured to the revolving portion of the turret, 
down through the space between decks to the protective decks of 
the ship, so that the turret roof, front, and side plates, together 
with the barbette and protective-deck armor afiford protection to 
the guns and machinery within. 

390. The turret-revolving structure is rotated by the training- 
gear machinery driven by an electric motor and universal speed 
gear. (See paragraph 402 .) The driving end of the speed gear 
connects directly to the worm shaft which drives the worm wheel 
attached to the training pinion shaft. The training pinion (see 
Plate IV) which is secured directly to the training-pinion shaft, 
meshes with the training rack secured to the turret roller path 
foundation. 

391. In the latest ships, two sets of worm wheels and pinions 
are used. The gears are driven by one main electric motor through 
a special arrangement of universal speed gears. The torque is 
transmitted from the motor to the training pinion direct without 
the use of friction discs, such as were used in the older turrets. 
In this case, the gear is designed with sufficient strength to with¬ 
stand the forces resulting from the firing of the guns, and the* 
inertia of the turret due to starting and stopping. 

392. Auxiliary training gear is provided for use in case the 
main electric motor or speed gear becomes disabled. This gear 
consists of a low-powered electric motor receiving current from 
storage batteries stowed in the revolving structure. The speed 
of train, as in the case of the main gear, is controlled through a 
small universal speed gear. Hand training is also provided for 
emergencies when power is not on the turret. This gear is not 
efficient, and is inadequate for training the turret, at any satis¬ 
factory speed, being merely provided as a last resort. 

393. The deck lugs, which contain the trunnion seats and cap 
squares, are heavy steel castings bolted to the gun girders. The 
gun girders form the supports for the deck lugs and elevating 


Naval Gun Mounts 


343 


gear; and through them the firing forces, at the trunnions, are 
transmitted to the roller path. (See Plate IV.) 

394. The gun slide, to which the trunnions are secured, sup¬ 
ports the gun and the recoil mechanism. The slide is of cast steel 
and is lined with bronze. The trunnions about which the guns are 
moved in ^elevation, are located approximately at the center of 
gravity of the oscillating weights which they support. In the 
latest turrets, these trunnions are of special form, designed to 
reduce the size of the port opening through the turret front plate. 

395. The recoil mechanism, consisting of the recoil cylinder 
and throttling rods, is attached to the slide. The piston rod is 
attached to the gun yoke and recoils with the gun. During recoil, 
the liquid in the cylinder is forced through the orifices formed 
between the throttling rods and the apertures in the piston. These 
orifices are so proportioned that the resistance to recoil is prac¬ 
tically constant for the whole distance, and of sufficient magnitude 
to check the recoil in the distance allowed. In the latest turrets 
one recoil cylinder is used with two to three throttling rods, 
depending upon circumstances. The method of computing the 
proper dimensions of throttling rods is discussed in the chapter 
on Recoil. 

The energy absorbed by the hydraulic brake results in a con¬ 
siderable heating of the recoil cylinder liquid. When the gun is 
fired rapidly, the heating efifect is accumulative and results in a 
considerable rise of temperature and expansion of the recoil 
cylinder liquid. This expansion, unless compensated for in some 
manner, interferes with the return of the gun to its battery posi¬ 
tion. The expansion of the liquid is therefore compensated for by 
means of an expansion chamber which has been provided for all 
turrets. By means of this chamber, space is provided for the 
expansion of the liquid and the capacity of the chamber is 
sufficient to meet all service requirements. This chamber is con¬ 
nected to the forward end of the recoil cylinder. It functions 
automatically, and requires no attention except the exercise of 
ordinary precaution, during the process of filling the recoil cylin¬ 
ders, to see that the expansion chamber remains empty. 

The recoil mechanism performs its primary function during 
recoil, but it has a limited efifect also on counter recoil. 



344 


Naval Ordnance 


396. The counter-recoil mechanism which is also attached to 
the slide, is provided for the primary purpose of returning the 
gun. to the battery position at all angles of elevation, and although 
this is its primary function, it has a limited effect on recoil. 

Until recently, the force for returning the guns to battery was 
derived from the compression of helical springs, but on account of 
the large increase of the recoil weights and the angles to which 
guns are now elevated, springs are impracticable on account of 
the limited amount of work that can be stored up in a spring 
system. The return of the gun to battery in the latest mounts is 
accomplished by compressed air. 

This system (pneumatic) is not subject to the same limitations 
as the spring system, since the pressures and dimensions of the 
counter-recoil cylinders can he increased to the proper amount. 
The initial air pressure varies from 800 pounds to 2000 pounds 
per square inch. This pressure is held indefinitely without leakage 
by the special packing used. Upon returning to battery, the 
recoiling weights are brought to rest by means of a counter-recoil 
plunger and dash pot which operates in the same manner as 
described for the recoil cylinder proper. With the parts properly 
designed, the guns return to battery without shock. 

397. The elevating gear (see Plates III and IV).—In the latest 
turrets the guns are arranged to elevate independently. Under 
normal conditions, however, all three elevating gears are locked 
together by clutches so that all guns elevate together. The ele¬ 
vating gear provided for all guns is similar. Sufficient power is 
provided in each set so that all three guns may be operated by any 
single set of electric and hydraulic motors. In case of a casualty 
which would increase the resistance imposed upon the elevating- 
gear, the guns may be elevated with all three electric motors and 
speed gears operating simultaneously. The elevating gear for 
each gun consists of an electric motor driving a universal speed 
gear. The “ B-end ” of the speed gear connects to the elevating 
nut which drives the elevating screw attached to the slide. The 
elevating nut is supported by the oscillating bearing which in turn 
is supported by the transom casting attached to the turret struc¬ 
ture. Rotation of the elevating nut imparts an up-or-down 
motion to the elevating screw depending on the direction of rota¬ 
tion of the nut. 


Naval Gun Mounts 


345 


The rate and amount of elevation of the guns is controlled 
through a two-hand drive connecting to the control shaft of 
“ A-end ” of the hydraulic-speed gear. This two-hand drive is 
located in a convenient position with reference to the sight tele¬ 
scope and gun-pointer’s seat, so that the gun pointer may keep his 
eye on the telescope for all positions of the gun in elevation. 

The “ follow-up ” type of control is used; one turn of the hand 
wheel produces a definite angle of elevation of the gun; and the 
direction of rotation of the gun about the trunnion axis corre¬ 
sponds in direction, to the direction of rotation of the hand wheel. 
A definite ratio also exists between the rate of rotation of the 
hand wheel and the rate of elevation of the guns, and when the 
hand wheels come to rest, the gun is brought to rest. With the 
type of control described the guns can be operated with the same 
facility as a hand operated mount. 

398. The training-gear control also has a similar “ follow-up ” 
arrangement. 

399 . Powder supply (see Plates III, IV and VI).—The powder 
is stowed in the powder magazines in air-tight powder tanks. In 
supplying powder to the guns the powder is taken from the tanks 
and passed through flame-proof scuttles in the magazine doors to 
the powder-handling room. From this point the powder is carried 
by hand to trays located at the lower end of the powder conveyor. 
The trays rotate with the revolving portion of the turret and main¬ 
tain a fixed relation to the hoist. From the trays in the lower 
handling room the powder bags are fed into the receiving end 
of an endless-chain conveyor hoist. Two hoists of this type are 
used. These hoists deliver the powder bags to the trays located 
in the upper powder-handling room beneath the pan separating the 
turret gun chamber from this room. One charge for each gun is 
assembled in this room for transmittal to the guns as required. 

From the upper powder-handling room, the powder bags are 
loaded into the upper powder cars which convey the powder from 
the upper powder room to the breech of the guns. One powder 
car is provided for each gun, and each car is arranged to carry a 
complete charge per trip. The charge is hoisted while the shell is 
being rammed into the gun. The powder car is flame-proof so 
that the charge is completely protected from flare-backs until the 
bags are dumped out into spanning trays prior to being rammed 




346 


Naval Ordnance 


into the gun. The upper powder hoist is of a reciprocating type, 
hydraulically operated. An “ A-end ” of speed gear serves as a 
pump and delivers liquid under pressure. The motion of the car 
is controlled by the movement of the control screw of the speed 
gear. Flame-proof doors form a seal between the upper powder¬ 
handling room and the gun chamber of the turret, so that there 
can be no direct communication at any time between the gun 
chamber and the upper powder-handling room. 

In case power is not available for hoisting powder, the powder 
bags may be hoisted from the lower handling room to the upper 
powder-handling room by means of a whip hoist provided. Upon 
arrival in the upper powder-handling room the powder bags are 
passed through hatches in the upper powder hoist trunk to the 
breech of the gun by hand. Platforms are provided for the use 
of the powder-passing crew. 

400. Shell hoists (see Plates III, IV and VI).—The shell 
hoist, which is a standard navy type, extends from the shell¬ 
handling room, located directly below the upper powder-handling 
room, to the gun chamber, at a point opposite the breech of each 
out-board gun. Two hoists are used. Shells are stowed on plat¬ 
forms in the turret foundation space and in the shell-handling 
room. The shells are stowed in both positions on their bases in 
such a way that one shell can be removed from its fastenings with¬ 
out disturbing the adjacent shells. The shell is parbuckled from 
its stowed position to the hoist by means of a manila rope running 
over a winch driven by the shell-hoist motor. 

From its position in the lower end of the shell hoist the shell 
is raised by a series of short strokes to the gun chamber above. 
At the termination of each stroke a shell arrives at the gun and 
another shell is loaded into the hoist. The hoist is hydraulically 
operated by means of an “ A-end.” of a hydraulic speed gear. The 
speed gear which acts as a pump delivers liquid under pressure to 
a ram which actuates a rack bar and pawls which raise the column 
of shells in the hoist. During the return stroke of the ram the 
shells are supported by a series of pawls fixed to the shell tube. 
The motion of the hoist is controlled through the control screw of 
the hydraulic speed gear. The shells are dumped out of the upper 
end of the hoist by means of a cradle from where they are rolled 
to the guns. 


CHAPTER X. PLATE III. 


l: 


\4-Z) GUN TURRET 

UOHCITUDINAL 

jECTion 


*7 SHELLS »M 
P»SSACE WAY 
__! 1 ST.-PL AT FOR M 


HOLDING DOWN 




































































































































































































































































1 

























CHAPTER X. PLATE IV. 


To (KAB TV^ 


T)£CH 

Roll Ed 
ROLLER PATH- 


TRAINING PlNNl 5N- 


FOUNDAT ON' 


$un 


14 - m 3 GUN TURRET 

TRANSVERSE 

SECTIONS 



























































































































































































































































































































































































CHAPTER X. PLATE VI. 























































































































































348 


Naval Ordnance 


When power is not available in the turret for running the shell 
hoist, shells may be hoisted to the turret chamber by means of a 
chain purchase using an auxiliary tube. 

401. Rammer and spanning tray (see Plate VI).—The shell 
and powder charge are rammed into position in the gun by means 
of a chain rammer. The guns are loaded at a fixed loading angle. 
After opening the breech, the spanning tray is carried forward 
from its folded position, at the forward end of the rammer, so as 
to extend into the chamber of the gun. The shell is then rammed 
from its position in the rammer tray to its position in the gun by 
means of a chain. After loading the gun the tray is folded back 
clear of the recoil position of the gun. The rammer head is 
attached to the end of the chain that comes in contact with the 
shell, and is provided with hydraulic buffers to relieve the rammer 
mechanism of shock. The chain is contained in a rammer casing 
and is driven by a sprocket which in turn is driven by a hydraulic 
speed gear. Motion is controlled through the control shaft of the 
speed gear, so that the speed may be varied, as required. 

The Waterbury Hydraulic Speed Gear. 

402. The Waterbury hydraulic speed gear (Plates VII and VIII) 
is a machine for transmitting rotary power at variable speeds 
and in either direction without steps or abrupt gradations, while 
the source of power rotates continuously in one direction without 
any necessary change of speed. This source may be an engine of 
any kind, an electric motor, a shaft or any rotating mechanism 
from which it is desired to transmit power. The medium of 
transmission is oil. This being practically incompressible, the driv¬ 
ing is very positive, except to the extent of the very slight leakage 
necessary for lubrication. 

403. “ A-End ” and “ B-End.”—Functionally the machine con¬ 
sists of two separate mechanisms designated, respectively, the 
A-end and the B-end. 

The A-end is an oil pump operated by the driving power, what¬ 
ever that may be. Its function is to deliver oil to the B-end at any 
required pressure and receive it back again, thus keeping up an 
oil circulation. The A-end contains a controlling device by which 
the quantity of oil delivered to the B-end is regulated exactly to 
meet the speed requirements of the B-end. The shaft of the 


CHAPTER X. PLATE V. 



1 

2 

•WORK SHOP 

Overhang turret 

3 

BREECH Or EACH GUN 


SHELL HANDLING ROOM 

5 

POWDER HANDLING ROOM 

6 

LOWER HANDLING ROOF) 

T 

TRAINERS T POINTERS 

© 

SHELL HANDLING ROOM 


9 TO OTHER TURRETS OF SAME GROUP* 

JO TO PLOTTING ROOM FROM RflHGtT FINDER 

I l l- TQ 3 VB 


HoTC: - ALL voice: tubes turned 
thro angle or 90° insoaro 


14 ,N 3 GUN TURRET 

TURRET OFFICERS* 
I STATION 










































































































I 



Naval Gun Mounts 


349 


A-end is supposed to rotate in one direction only, at a constant 
speed. 

The B-end is a hydraulic engine. Its rotating parts are almost 
exactly like those of the A-end. In its capacity as an engine its 
shaft rotates at any speed and in either‘direction in exact obedi¬ 
ence to the quantity and direction of delivery of the oil it receives 
from the A-end. 

404. Arrangement of the Ends.—When conditions permit, the 
two ends are united into one machine, a middle partition, called a 
<valve plate or midplate, separating the two parts. If the two shafts 
are to stand in a straight line, the valveplate is a flat disc with 
parallel faces. If, however, the shafts are to stand in any other 
position than a straight line, the shape of the valveplate may be 
varied to meet the requirements. 

The conditions of installation may be such as to require the 
locating of the A- and B-ends some distance apart. Each end will 
then have its own valveplate, which may be appropriately termed 
an “ endplate.” The two endplates will have their two main.oil 
passages connected by two pipes. Since the chief function of the 
valveplate or endplates is to furnish passages for the circulation of 
oil between the two ends of the gear, it is evident that the connect¬ 
ing pipes may be so bent as to make the possible variety of arrange¬ 
ments unlimited. 

405. Description.—To simplify the description let us consider 
only the unitized or C-type of machine wherein the shafts are in 
line with each other. 

The fixed or non-rotating parts, which do not rotate with the 
shafts in the transmission of power, are the cases, the valveplate,. 
the tilting box, the angle box and the control shaft. 

All the working parts of the machine are enclosed within cylin¬ 
drical shells, called cases, one for each end of the machine. The 
open, or large, ends of the cases are securely bolted against the 
opposite faces of the valveplate by long bolts passing through the 
cases and the valveplate. The other ends of the cases are closed 
into form hubs through which the shafts extend. Legs cast on the 
cases provide means for securing the machine to its support. 

Thus combined the cases form an oil reservoir within which the 
active parts rotate. The greater portion of the oil is not under 
pressure, but is in communication with the air through the oil 


350 


Naval Ordnance 


expansion box on top of the case. The only active oil, which is 
directly used in transmitting the power, is enclosed within the port 
passages of the valveplate and within the cylinders ahead of the 
pistons. 

406. Valveplate or midplate is a very important element of the 
machine. On each of its faces is carefully prepared a contact 
surface against which the face of a cylinder barrel slides in its 
rotation. Through these surfaces are two semi-annular passages, 
called valveplate ports, otle in each half of the plate, extending 
from the A-face to the B-face, through which the oil circulates 
when transmitting power. Between the ports both at the top 
and the bottom are Hat faces called lands, into which are cut short 
reduced extensions from the ports. As the cylinder barrel rotates, 
the cylinder ports pass in succession across these lands and the 
contents of each cylinder is for the moment imprisoned within the 
cylinder while being carried across from one port to the other At 
the center of the valveplate are bearings for the inner ends of the 
shafts. Several valves are also located in the valveplate, which 
will be described further on under the heading ‘'minor parts.” 

407. Tilting Box and Angle Box.—The purpose of the tilting 
box in the A-end is to carry a thrust roller track against which the 
socket ring may rotate in a plane at any desired angle to its shaft. 
In the earlier designs there were two tilting boxes, one in each end 
of the machine, but later the B-tilting box was displaced by a 
wedge-shaped casting, called the angle box, carrying its roller 
track at an angle of about 20 degrees from perpendicular, and 
screwed securely to the end of the inside of the B-case. This sub¬ 
stitute for the tilting box is possible for the B-end, since the angle 
is not changed after once being set. But in the A-end the tilting 
box must be retained for the reason that the speed and direction of 
rotation of the B-end are controlled by changing the angle of the 
tilting box. The tilting box is suspended, and may be oscillated, 
on two trunnions, which are formed on the box itself and which 
bear in bronze bushings set in the sides of the case. An elongated 
hole is cut through the bottom of the box so as to give a free 
passage for the main shaft even when the box is tilted to its maxi¬ 
mum angle. The box is retained in its bearings by two tilting box 
retaining trunnions which are screwed through from the outer 
sides of the case and enter bushed holes in the box. 


Naval Gun Mounts 


35 ' 


Projecting from the bottom of the box are four fingers or prongs 
forming guides or slideways for the guide blocks connected with 
the control shaft. 

408. Control shaft.—The purpose of the control shaft is to tilt 
the tilting box on its trunnions either way from the neutral or 
perpendicular position according to the direction and speed re¬ 
quired of the B-shaft. It is a threaded shaft provided with a 
thrust flange, or collar, made integral with the shaft. This flange 
bears between two fibre thrust rings, the under one of which rests 
in the control shaft hanger. The upper one is adjusted against the 
flange by the control shaft bearing, which is screwed into the 
hanger and locked by the bearing nut. The hanger itself is screwed 
into the threaded mouth of the hanger housing, which forms a part 
of the case. The lower end of the control shaft bears very freely 
in a socket in the control shaft-guide plug, which is screwed into 
the bottom or lower end of the housing. 

The threaded portion of the control shaft carries a trunnioned 
nut, whose trunnions carry four guide blocks, two on each 
trunnion. The outer two of these blocks slide in guideways 
planed in the sides of the housing. The inner blocks slide between 
the fingers of the bottom of the tilting box. 

The turning of the control shaft causes the trunnioned nut to 
move up or down, carrying with it the fingers of the box. The 
angular positions of the tilting box are therefore determined by 
the rotation of the control shaft. 

409. The rotating parts of the A- and B-ends are alike except 
the location of the sockets in the socket rings and of the cylinders 
and ports in the cylinder barrels. We may, therefore, confine our 
attention to one end only. These parts are so assembled upon the 
shaft as to form what may be called a shaft group, comprising the 
shaft, the cylinder barrel with the keys that connect it with the 
shaft, the socket ring with the universal joint that connects it with 
the shaft, and the pistons and connecting rods. 

410. Shafts.—The A- and B-shafts are alike. Bushings in the 
hubs of the cases form the main bearings, while the inner ends of 
the shafts are provided with roller bearings in the valveplate. I he 
ends of the two shafts are separated in the valveplate by a fiber 
disc called the inter-shaft disc. At the intersection of the plane of 
the socket ring the shaft is formed into a closed yoke around the 
universal-joint parts described under universal joint. 


352 


Naval Ordnance 


Where the shaft passes through the barrel it is flattened on two 
sides and perforated to receive the barrel keys and is threaded to 
receive the barrel nut. 

The barrel nut performs no other function than to prevent the 
barrel from sliding off the shaft when the assembled group of 
shaft, barrel, and socket ring are being handled. When the gear 
is fully assembled and in operation the barrel does not touch 
the nut. 

411. Cylinder barrel.—The cylinder barrel contains nine cylin¬ 
ders. It is loosely attached by two keys provided with pivots fitting 
loosely in a hole through the shaft. The loose fit of the barrel on 
the shaft together with the pivoted keys gives it a slight freedom 
of motion so that its face can rest squarely against the face of 
the valveplate. Moreover, it can slide freely endwise along the 
shaft. This endwise motion is aided by a barrel spring backing 
against a flange on the shaft. The purpose of the spring is to hold 
the barrel against the valveplate when not in operation. When 
the oil is under pressure, the barrel is held against the valveplate 
automatically by reason of the fact that the cylinder ports are 
smaller than the pistons, giving an excess internal pressure, forc¬ 
ing the barrel towards the valveplate. 

The cylinder barrel and keys do not transmit any of the working- 
torque. 

412. Pistons.—There are nine pistons in each barrel, the pis¬ 
tons and cylinders being ground and lapped to a smooth working 
fit without any packing. Narrow shallow grooves are cut around 
the pistons, which serve to interrupt the leakage stream lines and to 
trap dirt. 

413. Connecting rods.—Each piston is connected to the socket 
ring by a connecting rod. The rods have perfectly spherical ball 
ends of unequal diameters. The smaller end is secured into a 
socket formed in the piston, which it fits perfectly, by a bronze 
split piston-socket bushing which is secured in place by a finely 
threaded piston-socket cap. 

The main purpose for having one ball end smaller than the 
other is to make it possible to string the ring-socket cap and the 
piston-socket cap over the smaller end; the smaller ball is held 
from being drawn back through the piston-socket cap by the split 
bushing. 


Naval Gun Mounts 


353 


The large ball end is secured in a socket in the socket ring by 
the ring-socket cap. 

Through the end of the piston and through the whole length of 
the connecting rod is a small hole which feeds oil under pressure 
from the active oil system to lubricate the balls and sockets. 

414. Socket ring.—The socket ring has cut into it nine sockets 
fitted with bronze ring sockets against which rest the large ball 
ends of the connecting rods. These sockets are unequally spaced 
to correct certain irregularities of the universal joint. 

The back of the socket ring is provided with a chrome-venadium 
roller track which has two roller faces, one for the main conical 
thrust rolls and the other for the diagonal thrust, or cylindrical, 
rolls. 

The body of the socket ring extends inward in four arms form¬ 
ing slots, or key-way shaped pockets, into which the bronze main 
shaft trunnion-bearing blocks are secured by the main shaft 
trunnion-bearing block screws. 

415. Universal joint connects the shaft and socket ring. This 
joint consists of a shaft trunnioned block oscillating with the main 
shaft pin in the yokes of the main shaft. The trunnions of the 
trunnioned block operate in the bronze bearing blocks secured in 
the socket ring as mentioned above. 

The entire working torque of the gear is transmitted through 
the socket ring, the universal joint trunnions, and the main shaft 
pin. 

MINOR PARTS. 

416. Replenishing valves.—There is necessarily a small amount 
of leakage of oil from the high pressure active portion into the 
inactive body of oil enclosed in the cases. Provision must be made 
to replace this leakage as fast as it occurs, otherwise there would 
be a vacuum in the cylinders and port passages. For this reason 
there are two check valves in the lower part of the valveplate called 
replenishing valves. One of these is connected with each port 
passage, and permits the oil to flow freely from the case space into 
the port passage, but prevents its flowing in the opposite direction. 

The valve itself is a steel ball. The seat is a steel piece screwed 
in from the outside. The hole in the valveplate through which the 
seat was inserted is closed by a plug called the replenishing-valve 

cap. 


24 


354 


Naval Ordnance 


417. Relief valves.—In the transmitting of power at very low 
speed in the B-end it is possible that the oil pressure may rise to 
thousands of pounds per square inch should the resistance to be 
overcome be correspondingly great. It is therefore necessary to 
provide safety valves to be set at any desired maximum pressure, 
say 1000 or 1200 pounds. Should the pressure exceed this amount 
the oil will escape from the high pressure port passage through a 
relief valve into the case space and flow back again through a 
replenishing valve into the low pressure port passage. 

The relief valve group consists of a valve, a spring, a plug, and 
adjusting washers. The plug forms the backing for the spring, 
whose compression is adjusted by the use of more or fewer copper 
washers under the head of the plug. 

418. Air valves.—At the highest points in the two port passages 
are needle valves. The purpose of these is to allow any air that 
may be imprisoned in the passages to escape into the case space, 
whence it can rise through the oil expansion box. It is only neces¬ 
sary to open these valves one or two turns during the filling process, 
after which they are to be closed tight, and perform no other 
function. 

Thimble caps are screwed over the ends of these valve screws to 
prevent oil from leaking out or air from being sucked in. 

419. Oil expansion box.—As the proper functioning of the 
machine requires that the medium of power transmission be prac¬ 
tically incompressible, it is important that no air be allowed to mix 
with the oil. The case must therefore be entirely full of oil. To 
meet this requirement fully it is necessary to have the oil in the 
machine connected with an external supply that will always be in 
communication with the interior and yet not permit the entrance of 
air. The oil expansion box serves this purpose. In the illustrations 
the box is represented as connected directly with the top of the 
case. In practice, however, the box may be located in any con¬ 
venient place near by and connected with the case by a pipe. The 
connections should always be such as to allow the easy escape of 
air from the case. 

In the lid of the box will be noticed a baffle. Immediately above 
this are holes in communication with the outside air. The baffle 
prevents the splashing of the oil in the box from stopping the air 
holes, should there be a sudden rush of oil from the case into the 


Naval Gun Mounts 


355 


box. This is an interesting and important phenomenon. Should 
the machine become overloaded, the flow of oil through the relief 
valve is more rapid than the supply through the replenishing 
valve for the reason that the relief valve is acting under high pres¬ 
sure, while the replenishing valve is acting only under atmospheric 
pressure. A momentary vacuum is produced in the active body 
of oil, which is the same in effect as if the whole volume of oil 
had suddenly increased. 

420. Stuffing boxes and packing.—Where the shafts pass 
through the cases there are stuffing boxes. These are of the 
ordinary type and need no special comment further than to call 
attention to the kind and shape of material used in packing. 
Leather cups of U-section are used, the U-channel being filled 
with pure asbestos yarn containing no paraffine, tallow, or wax 
filling. Two of these U-rings are used in each stuffing box. If 
they alone do not fill the box a sufficient quantity of asbestos yarn 
may be placed between the leather rings. 

In the threaded surface of the control shaft bearing is a groove 
which is to be filled with a leather strip called the control bearing 
thread packing. When the bearing piece is screwed into the hanger 
and the control shaft bearing nut is screwed down tight, this 
leather strip is compressed into the channel between the top of the 
hanger, the nut, and the bearing so as to prevent any leakage of oil 
or air. 

Where the end of the case fits against the valveplate, only a 
paper gasket is used. This is cut to fit that part of the face of the 
valveplate that comes in contact with the case. It is cemented 
onto the valveplate with a solution of shellac in alcohol. 

421. Plugs.—The various plugs need only to be mentioned. 
In the valveplate are two gauge plugs. These close holes connected 
with each port passage for the attachment of pressure gauges 
where desired. In the cases are plugs for drainage, escape of air, 
equalizing pipes, etc. 

HOW THE GEAR OPERATES. 

422. In order that the functioning of the various parts of the 
machine may be understood, let us assume that the gear is as¬ 
sembled and filled with oil ready for running. 


356 


Naval Ordnance 


The entire space within the cases and valveplate not actually 
occupied by metal is filled with oil. No air pockets exist, and 
in order that no air may enter the case, the oil is made to fill the 
expansion box about half full. A definite portion of the oil is 
enclosed within the cylinders ahead of the pistons and within the 
port passages of the valveplate. This is the really active portion 
of the oil, and if there were no leakage this is all the oil that would 
be used in transmitting energy. The inactive oil which fills the 
space within the cases is never under pressure. It is simply a 
supply for lubrication, into which leakage from the active oil 
may flow and from which this leakage is replenished through the 
replenishing valves, the total quantity remaining constant. 

With our attention directed to the A-end of the sectional views, 
let us first assume that the A-tilting box with its socket ring is 
set at the neutral position, that is, perpendicular to the shaft. 
Under these conditions the shaft in rotating will carry around with 
it the socket ring and the cylinder barrel together with the pistons 
and connecting rods, but the pistons will have no tendency to 
reciprocate in the cylinders. There will, therefore, be no drawing 
of the oil in or forcing it out through the valveplate. The only 
work done will be the stirring of the oil in the case by the revolving 
parts and the light friction of the shaft bearings and the sliding of 
the face of the cylinder barrel against the face of the valveplate. 
The B-end will not be disturbed. 

423. If the control shaft be turned a little so as to move the top 
of the tilting box away from the valveplate and if the A-shaft be 
rotating over towards the observer, all the pistons, as they move 
up on the far side of the machine, will draw in oil through the port 
in the far side of the valveplate; all the pistons as they move down 
on the near side will slide in towards the valveplate and force the 
oil through the port in the near side of the valveplate. The near 
port will thus be under pressure while the far port is in suction. 

It should be noticed that when a piston reaches the top or higher 
position, in its revolution, it for an instant makes no end movement 
and the oil in that particular cylinder is carried across the “ Land,” 
or space between the two valveplate ports, from the suction side 
to the pressure side. The same condition exists when a cylinder is 
passing its lowest position, except that the piston is then at the 
inner end of its stroke and is passing from the pressure side to the 
suction side. 


Naval Gun Mounts 


357 


The quantity of oil forced through the valveplate port depends 
upon the angle at which the tilting hox stands and consequently 
the length of the piston stroke. 

424. We have spoken of forcing the oil through the valveplate 
port, but this cannot take place unless there is some means acting 
to receive the oil and carry it across to the port that is under suction. 
This is the function of the B-end. The B-socket ring always stands 
at an angle of about 70 ° to the B-shaft, and when the B-shaft 
rotates the B-pistons will make their full stroke as they pass 
between the bottom and the top positions. Now, when the 
A-cylinders are moving down on the near side, as described above, 
oil is forced through the valveplate port of this side into the 
B-cylinders of the near side. But they cannot receive the oil unless 
their pistons move back to give space. This movement of the 
pistons communicated to the inclined socket ring through the con¬ 
necting rods causes the socket ring to rotate on its roller thrust 
bearing, and to carry the shaft around with it. The shaft in turn 
rotates the cylinder barrel keyed to it, and the whole group rotates 
in the opposite direction to the rotation of the A-shaft. 

425. The speed of rotation of the B-shaft depends upon the 
quantity of oil it must take care of. The B-socket ring being 
always set at its maximum angle gives the pistons their full stroke. 
If each cylinder has a capacity of say 3 cubic inches, the revolving 
of all nine of the B-cylinders would transfer 27 cubic inches of oil 
from the near side to the far side. If now the control shaft of the 
A-end be turned so as to tilt the A-socket ring only a little, say 
enough to reciprocate each piston to the extent of 1-100 of a cubic 
inch, all nine of the A-cylinders will together transfer 9-100 cubic 
inches of oil from the far side to the near side at each rotation of 
the shaft. Since the capacity of the B-cylinders per rotation of 
the B-shaft is 27 cubic inches, 300 rotations of the A-shaft will be 
necessary to rotate the B-shaft once. If the A-socket ring be tilted 
still further, the B-shaft must rotate proportionately faster. The 
speed of the B-shaft is thus dependent upon the angle through 
which the control shaft has been turned. 

426. We have thus far spoken of the A-socket ring as tilted in 
one direction only. If it be tilted in the opposite direction, that is, 
with the top towards the valveplate, and the A-shaft still rotates 
in the same direction as before, the oil will be sucked in from the 


358 


Naval Ordnance 


near port of the valveplate and carried under across the lower 
land to the far side. This will, of course, cause the B-shaft to 
rotate opposite to its former direction, that is, in the same direction 
as the A-shaft. 

The Oil Pressure. 

The pressure of the oil in the valveplate passage depends upon 
the resistance offered to the turning of the B-shaft and not upon 
the speed. The pressure rises instantly to meet any resistance up to 
the capacity of the driving motor. If the A-socket ring stands 
almost perpendicular to the shaft, only a very small quantity of oil 
is transferred per rotation, which has the effect of giving a very 
great leverage, and even a small motor may produce a pressure of 
several hundred pounds, and, of course, a corresponding torque 
or turning effort on the B-shaft. The actually permissible pres¬ 
sure in any particular machine depends upon the strength of the 
parts, but is limited by the setting of the relief valves. 


CHAPTER X. PLATE VII. 



Fig. 4. —Internal Parts. 


A Face.) 


THE UNIVERSAL SPEED GEAR, TYPE C. 













CHAPTER X. PLATE VIII. 


TILTING BOX TRUNNION 
TILTING BOX TRUNNION BUSHING- 
CONTROL GUIDE BLOCK, OUTER- 
CONTROL GUIDE BLOCK, INNER- 
CONTROL TRUNNIONED NUT- 

CONTROL SHAFT- 

SHAFT GLAND PACKING- 
'A SHAFT 1 DRIVING I- 


CFTTIRMAI Dl AM 


CASE PLUG 
CYLINDER BARREL 
PISTON 

PISTON SOCKET BUSHING 

PISTON SOCKET CAP- 

CONNECTING ROD 
TILTING BOX 
CONTROL SHAFT GLAND CAP- 
CONTROL SHAFT BEARING- 
CONTROL SHAFT BEARING NUT—, 
INTERMEDIATE RING BLOCK-, 
SHAFT GLAND CAP LOCK 
SHAFT GLAND CAP 
SHAFT GLAND 


PLUG FOR RELIEF VALVE PLUG 
RELIEF VALVE PLUG 
RELIEF VALVE 
RELIEF VALVE 
RELIEF VALVE 
CASE BOLT 
-ANGLE BOX DOWEL 


MAIN 

SHAFT 



WASHERS 

SPRING 


BARREL NUT 
MIDPLATE BUSHING 
INTER-SHAFT DISC (FIBER) 
MIOPLATE 

OIL EXPANSION BOX COVER 
OIL EXPANSION BOX BAFFLE 


-INTERMEDIATE RING 

-RING SOCKET NUT 

-SOCKET RING 

-SOCKET RING BALL RACE 

-THRUST BALL SEPARATOR 

-THRUST BALI 

-ANGLE BOX BALL RACE 


CYLINDER BARREL SPRING 
CYLINDER BARREL SPRING PIN- 
BARREL KEY PIN 
CONTROL SHAFT THRUST SCREW- 
BARREL KEY 
DRAIN PLUG 



TRANSVERSE SECTION 
OF MIDPLATE. 


CONTROL SHAFT 
CONTROL SHAFT GLAND CAP 
CONTROL SHAFT BEARING 
CONTROL SHAFT BEARING NUT 
AIR VALVE. 

GAUGE HOLE PLUG 
MIOPLATE PORT 
MIDPLATE BUSHING 
CASE BOLT 

INTER-SHAFT DISC (FIBER) 

RELIEF VALVE WASHERS 

RELIEF VALVE PLUG 

PLUG FOR RELIEF VALVE PLUG 

RELIEF VALVE 

RELIEF VALVE SPRING 

REPLENISHING VALVE BALL STOP PIN 

REPLENISHING VALVE BALL 

REPLENISHING VALVE SEAT 

REPLENISHING VALVE PLU G 

MIDPLATE 


FIG. 3 


■RAISEO ANNULAR SURFACES 
-CYLINDER 
— SOCKET FOR BARREL SPRING 
r-KEY WAY 
-CYLINDER PORT 


THRUST ROLLER TRACK- 


“ A ” end 


FIG. 2 

SECTIONAL ELEVATION 


-SCREW FOR ANGLE BOX 
-B" SHAFT (DRIVEN) 
-SHAFT PIN 
-ANGLE BOX 
SOCKET RING TRUNNION 
-REPLENISHING VALVE PLUG 



HANGER 



CONTROL SHAFT 
CONTROL SHAFT GLAND CAP 
CONTROL SHAFT GLAND 
CONTROL SHAFT PACKING 
CONTROL SHAFT BEARING 
CONTROL SHAFT BEARING NUT 
PACKING 

CONTROL SHAFT THRUST RING 
CONTROL TRUNNIONED NUT 
CONTROL GUIDE BLOCK, INNER 
CONTROL SHAFT THRUST SCREW 
CONTROL SHAFT THRUST DISC 
TILTING BOX 


“ B ” end 

THE UNIVERSAL SPEED GEAR. 


'A' CYLINDER BARREL 
AS SEEN FROM MIDPLATE. 
FIG. 4 


SCREW NUT TYPE 
OF CONTROL SHAFT 
FIG. 5 





























































































































































































































































































































.. ■ 














CHAPTER XI. 

BREECH MECHANISMS. 


427. Definition.—A breech mechanism is a mechanical device 
for closing the rear end of the chamber or bore of a breech-loading 
gun. The term includes the breech block or plug, all mechanism 
contained in or with it, and necessary operating gear. 

428. Requirements for a breech mechanism.—The following- 
may be said to be the principal requirements for a successful breech 
mechanism: 

1. Safety.— To be safe: (a) The gas must be prevented from 
escaping to the rear; this sealing, or obturation, must be auto¬ 
matic, greater pressure increasing the sealing or obturation, (b) 
The breech of the gun must not be weakened by the fitting of the 
breech mechanism, (c) The parts must have ample strength to 
prevent any portion from being broken or blown to the rear. 

(d) The danger of premature discharge must be minimized. 

(e) The breech block must be securely locked to prevent opening 
on firing. 

2 . Ease and rapidity of working.—This is necessary for rapid 
and continuous fire. Hence, this should include facility of load¬ 
ing, and certainty of extraction for rapid-fire guns. 

3 . Not easily put out of order.—In other words, it must be 
able to meet service conditions and hard usage. Parts should 
have a reserve of strength. All parts of the mechanism should be 
so designed as to be protected against injury. 

4 . Ease of repair.—Parts most exposed to wear should be so 
designed as to permit being easily replaced. This should also 
include accessibility of parts, so that breakage of any part will 
not disable the mechanism for any length of time. 

5 . Interchangeability.—Not only should individual parts be 
made interchangeable by accurate workmanship, but the whole 
mechanism should be capable of being mounted on similar guns. 
This is necessary to meet service conditions. 

429. The breech block or plug is the movable piece closing the 
breech of a gun. In most built-up guns it is carried by the jacket; 


359 


36o 


Naval Ordnance 


in the latest large guns, however, it is carried within a screw-box 
liner, or bushing. The above term applies to any shape of piece, 
or for any system of closure. 

430. In small arms and certain special guns, the term breech 
“ bolt ” is often used, instead of “ plug ” or “ block,” and “ breech 
action ” is a better term in this case than “ breech mechanism.” 

431. Systems of breech mechanism.—There are six principal 
systems of breech blocks in use, viz.: (i) The interrupted scrczv, 
( 2 ) vertical sliding wedge, ( 3 ) horizontal sliding wedge, ( 4 ) com¬ 
bined sliding and rotary system, ( 5 ) rotating eccentric block, and 
( 6 ) the sliding-bolt system. 

432. The interrupted-screw system is, in general, used in the 
navy for all guns of and above 3 inches in caliber. Secondary 
rapid-fire guns use systems ( 2 ), ( 3 ) and ( 4 ). Rotating eccentric 
blocks ( 5 ) are used by the navy for cartridge case guns. Military 
rifles, as well as certain automatic guns and machine guns, gen¬ 
erally, use the sliding-bolt system. 

433. Special guns, such as automatic guns, machine guns, etc., 
more properly use a “ breech action,” in which the different steps 
in closing the breech and operating the entire mechanism are very 
intimately connected. The system in these cases is defined by the 
name of the gun. 

434. The interrupted-screw system, also called “ slotted screw,” 
is divided into three classes: ( 1 ) French interrupted screw; ( 2 ) 
Els wick interrupted screw; and ( 3 ) Welin interrupted screw. 

435. In general, an interrupted screw plug is a plug which has 
two or more sections of the thread removed in the direction of the 
axis. Similar interruptions are made in the female thread of the 
screw box in the gun, in order that the plug may be entered or 
withdrawn in one motion and only a portion of a turn be given to 
lock or unlock the same in the screw box. 

436. The French interrupted screw was the most common 
system of fermeture, and was long in use. The breech plug, 
cylindrical in shape, has cut on its circumference a male thread, 
the character of which varies according to particular designs. It 
is then divided into a number of equal sections in the longitudinal 
direction (always divisible by two; usually six, eight or twelve), 
and the threads of alternate sections are then planed or slotted 
out. The female thread in the screw box is similarly slotted. In 


Breech Mechanisms 


361 


closing the breech, the threaded sections of the plug are brought 
opposite to the blank sections of the screw box ; the plug is pushed 
in either by hand, or by some mechanism, to the proper distance; 
and a fraction of a turn to the right or left is given, to interlock 
the threaded sections, the amount of turn necessary depending 
upon the number of threaded sections. Six threaded sections 
require 6 o° ; eight divisions, 45 0 , etc. The system is independent 
of the method of operating the mechanism. 

437. The Elswick interrupted screw differs from the French 
type, in that the forward part of the plug is conical and the rear 
part cylindrical. The threaded sections of the coned portion and 
the threaded sections of the cylindrical part are staggered. The 
advantages claimed for this arrangement are: ( 1 ) The working 
of the mechanism is facilitated, as the plug can be swung clear of 
the screw box without translation; ( 2 ) arrangement of the 
threaded sections distributes the strain around the entire circum¬ 
ference of the plug; ( 3 ) the cone-shaped plug increases the cross- 
section of the jacket at the forward end of the plug where the 
stresses in the gun are greatest. 

438. The Welin interrupted screw or “ stepped-thrcad " sys¬ 
tem has the block divided circumferentially into a number of 
groups of blanks and threaded sectors of increasing radius, so 
disposed that when the plug is unlocked the smaller threaded 
sectors of the plug clear the larger threaded sectors of the screw 
box. Each group of sectors consists of one blank and two or more 
threaded sectors. Three or four such groups of sectors are 
arranged around the circumference of the plug. This arrange¬ 
ment of threads gives a larger percentage of threads for a given 
length of plug and results in a lighter and stronger plug. 

439. The vertical sliding-wedge system, exemplified in the 
Hotchkiss and 3 -inch semi-automatic guns has a rectangular 
wedge-shaped block (containing the firing mechanism) that slides 
up and down in a vertical mortise within the square-shaped breech 
of the gun, guided by vertical ribs. It is moved by means of a 
crank, journaled in the right cheek of the mortise; a stud on the 
other end of the crank moves in a cam groove in the side of the 
block. The wedge completely closes the mortise when up, and 
gives only a sliding movement to the cartridge case in shoving it 

home. 


362 


Naval Ordnance 


440. The horizontal sliding-wedge mechanism is similar to 
the vertical sliding-wedge system except the block moves in a 
horizontal direction. 

441. The combined rotary and sliding-wedge system is ex¬ 
emplified in our service in the Nordenfelt 6 -pounder and 3 -pounder 
rapid-fire guns only. The breech block may be said to consist of 
two parts, the block and the wedge, the latter sliding on the front 
face of the former in the locking or unlocking movement; while to 
cover or uncover the bore, both rotate about a transverse axis, the 
top falling to the rear in opening. 

442. The sliding and rotary-block system.—In this system, to 
open the mechanism the block slides downward and is then 
rotated on a transverse axis, the upper part falling to the rear. 
This system is exemplified in our service by the Driggs-Schroeder 
guns. It has a rectangular block with rounded top, working 
entirely within the breech housing and is locked by means of 
collars on top of the block engaging corresponding grooves in 
the housing. The grooves are inclined slightly to the front, so 
the final movement in closing is upward and to the front, pushing 
home the cartridge case. The operation is through a cam within 
the block, moving against curved surfaces in the block’s recess: 
The cam is moved by a transverse axis. 

443. The sliding-bolt system.—In this system a more or less 
cylindrical piece, containing at least the firing pin and spring or 
hammer, moves longitudinally in a “ receiver ” attached to the gun 
barrel, and may be worked either by hand, as for small-arm rifles, 
or by certain mechanism, as in the Colt automatic gun. The bolt 
may have only a direct movement to the rear and front, giving 
the name “ straight pull,” or have a part attached which is turned 
for locking or unlocking, giving the name of “ turn bolt.” 

444. Types of ordinary systems of breech operation.—There 
are four types: ( 1 ) Service; ( 2 ) modified Farcot; ( 3 ) improved 
Fargot; ( 4 ) Naval Gun Factory design. The difference between 

( 2 ) and ( 3 ) is so slight that it is usual to class both under ( 2 ). 

445. Types of quick-acting breech systems: There are five 
principal types: ( 1 ) Rapid fire; ( 2 ) semi-automatic rapid tire; 

( 3 ) automatic rapid tire; ( 4 ) quick fire; and ( 5 ) machine gun. 

446. A rapid-fire breech mechanism is a quick-acting one, 
without a gas check. It is provided with an extractor and special 


Breech Mechanisms 


3 f >3 

firing mechanism for use in guns using a primed metallic cartridge 
case, or, in other words, for case guns. (See paragraph 156 .) 

447. A quick-fire breech mechanism is a quick-acting one 
provided with a gas check and a firing lock for use on guns where 
the charge is put up in bags and not in a metallic case, or, in other 
words, when loaded in bag guns. (See paragraph 155 .) 

448. There is, in reality, no distinction between the rapid fire 
and the quick fire, so far as the operating gear is concerned ; but 
the name is given because the gunS differ in their ammuntion, or 
rather in the manner of putting up the same. The breech 
mechanism differs, no extractor being necessary for the latter, but 
a firing lock is necessary. 

The term “ quick fire ” is apparently indiscriminately used 
abroad for guns having a quick-acting mechanism, whether using 
metallic cartridge case or powder charges in hags. It is well 
that a distinction should be made, as in the U. S. Navy, by the use 
of the terms “ case guns ” and “ bag guns.” 

449. Semi-automatic rapid-fire breech mechanisms are quick 
acting, part of the operation being by hand and part automatic. 
This gives rise to the name, both as “ rapid fire ” and as “ semi¬ 
automatic.” 

450. Automatic rapid-fire breech mechanisms are those in 
which all the operations are performed automatically by utilizing 
the energy of recoil. The name also defines the gun. 

The breech actions of machine guns are essentially quick 
acting, and their special features are the distinctive features of 
the gun. 

Systems of Gas Checks. 

451. Gas check.—This is a device to prevent the escape of the 
powder gas to the rear around the breech block or through the 
vent. 

452. The following are the principal characteristics governing 
the design of a gas check : 

1 . It should function at all temperatures that may be encoun¬ 
tered in service due to weather conditions, that is, from approxi¬ 
mately 5 0 to iio° F., and also be unaffected by the variations in 
temperature due to firing the gun. 1 emperature rises as high as 
200 ° F. have been observed when firing a 3 -inch rapid-fire gun. 

2 . The device should not adhere too strongly to its seat in order 
that the mechanism will function with ease. 


364 


Naval Ordnance 


3 . It should be elastic enough to conform to its seat, but also 
rigid enough so as not to be deformed to such an extent as to 
prevent successive functioning. 

4 . It should respond equally as well to the lowest as to the 
highest pressure developed in the gun. 

5 . It should exert a pressure on its seat greater than, or at least 
equal to, the gas pressure. 

To meet the above requirements it is necessary to consider, first, 
the type, and second, the application of the gas check. 

453. There are in general two types of gas checks, the plastic 
and the elastic. 

454. The advantage of the plastic gas check is that it conforms 
to any irregularities of its seat caused by erosion or accident. 

The disadvantages are the fact that it is apt to adhere to its seat 
too strongly, or to be deformed while the block is open with the 
result that the mechanism will not function with ease. Plastic 
materials do not possess a definite form, but conform easily under 
pressure to their seats. The pressure is transmitted equally in all 
directions, as in a fluid, and, to a greater degree than in elastic 
solids. 

The first plastic materials used for gas checks were fibrous 
materials such as cardboard or papier-mache. Experiments were 
also made with soap, but the soap liquefied due to the action of the 
heat. 

The materials actually in use are composed of about 65 per cent 
of a mineral fiber such as asbestos, and 35 per cent of tallow. The 
tallow keeps the gas check plastic and causes the fiber to flow 
under the action of the heat and pressure. 

455. An elastic gas check conforms to its seat under pressure 
except when small irregularities exist in the surface of the gas- 
check seat, hence the sealing depends upon the condition of the 
surfaces in contact. On the other hand, there is less tendency to 
adhere to its seat as the device returns to its original form as soon 
as the pressure is relieved, and it is not so easily deformed when 
the block is open. 

Elastic material may be divided into two classes, rigid and 
flexible, depending upon the resistance they offer to deformation. 
Steel is the most rigid and rubber compounds are the most flexible 
materials that have been used. 


CHAPTER XI. PLATE I. 


FIG. 1. INTERRUPTED SCREW. 

ALL MAIN BATTCAII3. 

«" PLUC.. 



FIG. 2. 8LIDING WEDGE. 


HOTCHKISS 8'TOH - 



FIG. 8. SLIDING AND ROTARY BLOCK. 

ontaas- schrococa s-pda- 



FIG. 4. COMBINED ROTARY AND SLIDING WEDGE. 

NOROENFELT 6POR. 




FIG. 6. SLIDING BOLT SYSTEM. U. S. MAGAZINE RIFLE. 


SYSTEMS OF BREECH-BLOCKS. 










































































































































































































































CHAPTER XI. PLATE II. 




THREE SYSTEMS OF INTERRUPTED-SCREW THREAD. 






































































































































































































Breech Mechanisms 


365 


Rubber compounds give a good seal for a few rounds, as they 
conform easily to their seats, but they are apt to adhere to the gun 
or block which makes it difficult to operate the breech mechanism. 
They are sensible to variations in temperature, being too soft at 
high and too hard at low temperatures. They are also attacked 
by the powder gas and oil. Elastic gas checks are made of copper, 
brass or steel. 

456. The methods of applying gas checks may be divided into 
three types: 

1 . Gas checks sealed by having an initial pressure on their seats. 

2 . Gas checks in which the pressure on the seat is built up auto¬ 
matically by the pressure of the powder gas. 

3 . Gas checks with an initial pressure on their seats but which 
pressure is increased by the action of the powder gas. 



Fig. 63. 


457. Type 1 . The Armstrong gas check, Fig. 63 , is an example 
of this class. AA is the gas check, B the block, and V a screw 
device for putting the initial pressure on the gas-check seats. 

The disadvantages of this gas check are due to the following: 
The gas check should be made of a material softer than its seat in 
order that it will conform to it, and it should be pressed against its 
seat with a pressure high enough to prevent the gas from escaping, 
as the action of the gas is to open the joint. On the other hand, 
the gas check should be hard enough so as not to be permanently 
crushed by the pressure of the gas. These are opposite character¬ 
istics and in reality the sealing of this device is poor and it is no 
longer in use. 



















3 6 6 


Naval Ordnance 


458. Type 2 . Automatic sealing. 

There are two methods of automatic sealing: by expansion, 
and by compression. 

(A) Scaling by expansion is obtained by the use of a metal 
cartridge case, Fig. 64 . The action of the gas is to expand the 
cartridge case against the wall of the chamber of the gun. The 
amount of this expansion being equal to the clearance between the 
case and chamber, plus the deformation, of the gun due to the 
pressure of the powder gas. The total expansion should n-ot ex¬ 
ceed the elastic expansion of the case, as otherwise the case may be 
permanently deformed or cracked and offer too much resistance 
to ejection. For this reason the metal should not be too hard or 
too soft. 



Fig. 64. 


When the charge is first ignited a small quantity of gas passes 
between the case and the wall of the chamber, but due to the 
small area and length of the channel, the resistance to its passage 
is high, and the pressure builds up so rapidly in the case that the 
sealing takes place very quickly. The surface in contact is so 
large that small local irregularities do not effect the seal. 

The case should be sufficiently thick at the base to prevent the 
metal from being forced into the joint between the breech block 
and the gun, but sufficiently thin at the mouth to insure easy 
expansion. 

(B) Scaling by compression is generally obtained by the use of 
a plastic gas check as in the de Bange system (Fig. 65 ). A pad of 




















Breech Mechanisms 


367 


plastic material, A, contained in an envelope, B, is held between 
the breech block, C, and the “ mushroom,” D, by the spindle of 
the mushroom which passes through the pad and breech block. 

The action of the gas pressure is to force the head of the mush¬ 
room to the rear, thus building up a pressure in the plastic material 
which is transmitted in all directions and presses the envelope 
against the wall of the gun. 



Let A— the area of the front surface of the head of the mush¬ 
room. 

A'— the area of the cross-section of the spindle. 

P — the gas pressure. 

P'~ pressure on the seat of gas check. 

N = a constant depending upon the plasticity of the gas 
check. The value of N for a fluid being 1 . 

Then 

P '_ NPA 
A-N " 

The values of N, and A, are made such that P', will be some¬ 
what greater than P. 

459. Plastic gas checks function very well when the gun is not 
fired too rapidly and with proper care a large number of rounds 
may be fired without changing the pad. On the other hand they 
are heavy and offer more or less difficulty to the installation of the 
firing mechanism and its safety features. 

























3 68 


Naval Ordnance 


460. The pads are made of a plastic material with a neat-fitting 
canvas cover. The edges are protected by split metal rings which 
expand due to the pressure transmitted by the pad. In some cases 
the front and rear faces of the pads are protected by metal discs. 

When the pads are to be used in guns where high pressures are 
developed, the pads are made as above except they are compressed 
in steel dies under a pressure from 50,000 to 80,000 pounds per 
square inch. After being subjected to this pressure they are no 
longer soft but possess a certain amount of elasticity, and may be 
said to be plastic-elastic. Due to this initial compression the recoil 
of the mushroom relative to the breech block is very small. 



Fig. 66.— The De Bange Gas Check, with Disks. Fig. 67.— The De Bange Gas Checi 

(Later form, showing split-rings.) 


bigs. 66 and 67 show the types of De Bange gas check used in 
the navy. 

461. To this group may be added the system shown in Fig. 68 
and experimented with in Spain. 

This system consists of a mushroom, A, which bears against a 
copper ring, B, of triangular cross-section. The pressure of the 
powder gas on the mushroom head causes the copper ring to 
expand and exert a pressure on its seats. It appears that this 
system should give good results. 

462. Type 3 . Gas checks with initial and automatic seal: 

In general, these gas checks (see Fig. 69 ) consist of a metal 
ling, h, adjusted to suit its seat in the chamber, with the diam- 





































Breech Mechanisms 


369 


eters of the ring slightly larger than those of its seat. By closing 
the block, the ring is forced to bear against its seat with a certain 
initial pressure. The profile of the ring is such that the pressure 
of the gas tends to press it against its seat. If it were not for 
the initial pressure, the pressure of the ring on its seat would be at 



Fig. 68. 



most only equal to the pressure of the gas, and gas would be apt to 
escape. With the pressure due to the gas added to the initial 
pressure, a seal is affected. 

The trouble with the above type of gas check is due to the 
difficulty experienced in adjusting the rings and making repairs 
due to erosion, which might result in the escape of gas. It is also 


25 



































3/o 


Naval Ordnance 


necessary to wash the rings frequently. The surface of the breech 
block, subjected to pressure, is increased, being equal to the area 
of a circle whose radius equals the radius of the gas-check seat. 
This radius is larger than the radius of the chamber. On the other 
hand, this check is light and does not take up much space in the 
gun, and lends itself easily to the installation of the firing mechan¬ 
ism with its safety features. 

Gas checks with initial and automatic seal may be divided into 
two sub-groups, those attached to the breech block, and those 
attached to the gun. 


Ou/st 



The first gas checks of this type were attached to the breech 
block in such a manner that they might be removed for cleaning 
and repairing, when necessary. 

The gas checks of older model French naval guns consisted of a 
steel gasket, Fig. 70 held to the breech block by a bolt passing- 
through the center of the gasket. The part of the chamber form¬ 
ing the seat was bored with a taper, the diameter at B, being 
slightly smaller than the diameter of the gas check which produced 
an initial pressure when the block was closed. The pressure de¬ 
veloped in the gun held the gasket pressed against the breech 
block and expanded the flange against the seat. The front edge 
of the flange was chambered to facilitate the expansion and lessen 
the adherence. 















Breech Mechanisms 


37 i 


In the older breech loading German guns the gas check con¬ 
sisted of a steel ring of triangular cross section, Fig. 71. The ring 
w as placed in the breech block with the inclined surface to the rear ; 
the piessure of the gas on the inclined face sealed the joint at b. 

'hhe disadvantage of this type is that the gas check is apt to be 
damaged when the block is open, and its use has been almost com¬ 
pletely discontinued. 

463 . Actually, gas checks of the initial and automatic sealing 
system are, in general, attached to the guns.; the first type used 
being the broadwell ring. 

Bneec* Block Gvsv 



J his consists of a ring of copper fixed in a seat machined in the 
powder chamber of the gun, Pig. 72. The diameter of the ring 
being a little larger than the diameter of its seat. When the 
breech block is closed this ring is seated with an initial pressure 
against a ring of the same metal fitted into the breech block. The 
initial seal is due to the pitch of the thread of the breech block. As 
the surface of the ring a, is very much less than the surface sub¬ 
jected to pressure of the gas check, the obturation is secured. The 
copper not being supple, expansion grooves are cut in the surface 
of the gas check and supporting ring. Fig. 73. If the gas escapes 
into the first groove it will expand with a drop in pressure and be 
less apt to escape to the second. Gas seldom escapes past this 
gas check when it is properly placed in its seat. 

464 . Mechanism for breaking the seal of gas checks and 
extracting cartridge cases: 

Gas checks tend to adhere strongly to their seats after guns have 
been fired and it is necessary to provide a special mechanism to 
loosen them before opening the breech. 












37 2 


Xaval Ordnance 


When cartridge eases are used it is necessary to provide a 
mechanism for extracting the case. This mechanism should be 
designed, first, to loosen the case by extraction, and second, to 
eject the case when the breech is fully open. 

With a gas check of the broad well ring type, the adherence of 
the gas check after the gun lias been fired is of a low order, and a 
large part of the initial efifort necessary to start the opening of the 
breech mechanism is due to the adherence of the threads of the 
breech block, and not the adherence of the gas check. This is an 
appreciable advantage of this type of gas check. 



When plastic gas checks are used it is necessary that the breech 
mechanism be designed so as to facilitate the breaking of the seal of 
the gas checks, which adhere strongly to their seats after the gun 
has been fired. In the first place it is necessary that the breech 
block may be rotated independently of the gas check, and secondly, 
that sufficient force may be exerted to translate the block and gas 
check to the rear. 

In the De Bange system the breaking of the seal is accomplished 
by passing the spindle of the mushroom through the breech block 
and placing a collar on the rear end of the spindle. A ball bearing 
is placed between the collar and the breech block (see Fig. 66). 
This arrangement permits the block to rotate without turning the 
gas check, but the collar causes the gas check to translate with the 
block, due to the pitch of the thread on the breech block. 














Breech Mechanisms 


373 

Jn some cases a spiral spring is also placed between the collar 
on the spindle and the breech block. J'his spring permits the 
breech block to be translated slightly as well as to be rotated inde¬ 
pendently of the gas check. 1 he compression of the spring is 
limited by a shoulder on the collar. J he force tending to break the 
seal is increased as the spring is compressed, and should the ad¬ 
herence be strong enough to hold until the shoulder on the collar 
comes into contact with the breech block, the seal will be broken 
as a force will build up quickly between the collar on the spindle 
and the breech block, due to the fact that the latter will be in 
motion. 

465. Extraction.— 1 he design of mechanisms to extract and 
eject cartridge cases varies with the particular design of the 
breech mechanism, but, in general, it consists of a lever which 
engages the rim on the cartridge case. This lever remains sta¬ 
tionary during the first part of the rotation of the block, the por¬ 
tion which engages the case is then moved slowly to the rear by 
means of a lever arm or cam surface which causes sufficient force 
to be exerted on the case to start it from its seat. The lever then 
becomes practically stationary until the breech is fully open; then 

. the lever is given a very quick motion to the rear with the result 
that the case is ejected clear of the gun. 

466. Locking the breech mechanism to prevent opening due 
to the shock of firing: 

Breech mechanisms in general cannot be opened by a pressure 
on the front face of the breech block, but there is a tendency for 
the breech mechanism to open, due to the shock of firing, and it is 
necessary to provide some form of positive lock. The design of 
these locks varies with the particular mechanism, but usually the 
lock feature is incorporated in the operating mechanism. The 
operating handle is latched in the closed position by the “ salvo 
latch ” which unlatches during the recoil of the gun. The salvo 
latch prevents the mechanism from being open after the gun has 
been loaded except when done so deliberately and with full knowl¬ 
edge that the gun is loaded. 

Firing Mechanisms. 

467. Definition.—The term ‘‘firing mechanism” is used to 
designate that part of the breech mechanism which directly ex¬ 
plodes the primer and thus fires the gun. 


374 


Naval Ordnance 


468. Guns are fired by percussion and by electricity. Percus¬ 
sion primers are used for guns of 3 -inch caliber and below, while 
guns of larger caliber use combination primers which may be fired 
either by percussion or by electric current. For large guns electric 
firing is considered preferable, percussion firing being used only 
as an alternative. 

Current for electric firing is furnished by batteries or by motor 
generators, connections being made so that either may be used as 
desired. 

469. Definition of percussion and electric firing mechanism.— 

A percussion firing mechanism is one in which the blow of a firing 
pin explodes the cap in a primer. 

An electric firing mechanism is one in which an insulated firing 
pin, suitably connected to a firing battery, or other source of 
electricity, transmits an electric current to the primer and heats a 
fine wire or bridge therein to a sufficiently high temperature to 
explode the charge of the primer. 

Generally speaking, for the percussion firing mechanism, the 
firing pin, surrounded by a spiral spring has a rectilinear axial 
movement within the plug, the “ cocking ” being performed either 
automatically during the opening of the breech mechanism, or, in 
continuous firing mechanisms, by hand. 

The electric firing mechanism has an encased insulated firing 
pin. The electric contact is not made until the breech block is 
nearly closed. 

470. The firing lock consists essentially of a receiver (that 
screws on the rear of the mushroom stem (see Plates III and X)) 
containing a “ wedge ” made so that the “ primer seat ” may be 
closed or unmasked for priming. The receiver has a suitable 
“ latch ” for locking, and “ extractor ’’ for ejecting the primer 
case, a “ firing bolt ” with spring, a “ sear ” and spring for holding 
the firing bolt “ cocked,” and a “ trigger ” to release the sear and 
to which may be secured a “ firing lanyard.” The wedge contains 
a “ firing pin ” and spring for percussion firing. The shank of the 
former is struck by the firing bolt, when released. 

471. Safety is one of the most important functions of a firing 
mechanism and special care must be given to it in design. In 
general, the safety features consist of devices which prevent the 
firing of the gun until the breech is entirely closed ; the details vary 
with each particular mechanism. 


CHAPTER XI. 


PLATE III. 



A Firing Lock Mounted on End of Mushroom Stem. 







I 


376 Naval Ordnance 

472. Definitions of firing attachments.—These are a part 
neither of the firing mechanism nor of the breech mechanism, but 
are certain appliances used to put in operation the firing mechanism. 
The firing lanyard, electric firing battery, wires, terminals, firing 
key, etc., are attachments. 

473. The two terms “firing mechanisms” and “firing attach¬ 
ments ” should not be confused. 

Description of Firing Lock, Mark XIV Mod. I. 

(Plates III, IV, VII and X.) 

GENERAL DESCRIPTION. 

474. This firing lock, which is the standard equipment for all 
the latest 5-, 6-, 14-, and 16-inch breech mechanisms, consists of a 
“ receiver,” “ wedge,” “ operator bar,” “ extractor,” and “ primer- 
retaining catch.” The wedge is actuated by means of a cam 
attached in the crank shaft of the breech mechanism. This cam 
withdraws the wedge and ejects the primer as the breech is opened. 
Priming is accomplished by hand, and in case of misfire, the lock 
can be reprimed without opening the breech mechanism by rotat¬ 
ing the wedge hand operating lever, thus lifting the wedge oper¬ 
ating plunger from the cam; the lock operator bar can then be 
drawn out, carrying with it the wedge. The wedge actuates the 
extractor and causes the ejection of the primer. After the new 
primer has been inserted, the lock operator bar is pressed in 
against its stop ; the wedge operating plunger re-enters the cam slot 
and gun is again ready to be fired. The firing lock is the same for 
all mechanisms; operator bars of different lengths, however, are 
necessary for the various breech mechanisms. 

475. The receiver, approximately rectangular in shape, is milled 
out to receive the wedge. It is secured to the breech mechanism 
by means of a bayonet joint on the end of the mushroom stem and 
is prevented from rotating, by the operator bar which is fastened 
to the wedge. The receiver is drilled for the extractor pin and 
necessary clearances are milled for the extractor. On one side 
of the receiver is milled a slot into which a lug on the hammer 
slides, thus preventing the hammer from being pulled back for per¬ 
cussion firing after the wedge has started to retract. In the front 
face of the receiver on the side with the milled slot is fitted the 


P.RIIECH Al ECU AN1SJIS 


377 


hammer guide block. This block is milled so as to align with the 
slot and allows the hammer to be cocked only when the wedge is 
fully closed. It also serves to lift the hammer, thus breaking the 
contact with the firing pin and preventing electric firing except 
when the wedge is fully closed. 

476. The wedge slides in the receiver and is operated by means 
of the operator bar. It is prevented from being withdrawn en¬ 
tirely from the receiver by means of a wedge-stop screw passing 
through the side of the receiver and fitting into a recess milled in 
the side of the wedge. The firing pin is mounted in insulating 
bushings at the inner end of the wedge. A hardened face plate is 
placed in the wedge next to the mushroom stem to take the thrust 
of the primer when fired. This wedge face plate has a striking 
lug for actuating the extractor as the wedge is retracted. The 
inner end of the wedge has a 45 0 sloping cut to permit of pushing 
the extractor home, and a circular tapered cut to seat the primer. 
The wedge is drilled for the hammer thrust pin and the firing 
spring. The thrust pin, when the hammer is drawn back, pro¬ 
trudes through the wedge into a hole drilled in the cross-head 
bearing of the breech mechanism. This hole is in alignment with 
th e thrust pin only when the breec h ■plug is Tu llv closed. 'The 
thrust pin, due to the action of the firing spring, keeps the hammer 
in contact with the firing pin except when the wedge is retracted. 
The wedge is secured to the lock operator bar by the operator bar 
pin passing through a hole machined in the outer end of the 
wedge. This hole is elongated to provide for any movement of 
the mushroom stem to the rear at the time of firing. 

477. The hammer has fitted into its right-hand side a spring 
catch which acts in conjunction with the cocking lever. 1 his catch 
engages with the latch as the cocking lever is pulled back by the 
lanyard for percussion firing until their relative positions are such 
that the hammer is released. When the lanyard pull is released, 
the cocking lever spring throws the lever forward into its original 
position and the latch snaps over the hammer catch. The contact 
piece is housed in an insulating housing in the forward end of the 
hammer. The lower end rests upon the firing pin when the lock is 
closed; the upper end carries a terminal to which one side of the 
electrical firing circuit is connected. 



3/8 


Naval ( )kdnance 


478. The cocking lever turns on the cocking-lever axle, 
directly above and in the same vertical plane as the axis of the 
hammer. Incorporated with the cocking-lever bearing is a cock¬ 
ing-lever spring which has a torsional action tending to throw the 
cocking lever towards the lock. One end of the spring engages a 
recess in its housing in the cocking lever, the other engages a hole 
in the torsional washer that serves as cover to the spring housing 
and also as a bearing for the cocking lever. Adjusting of the 
spring tension is effected by turning the torsional washer in the 
direction of the arrow stamped on it until the zero mark is aligned 
with the index line on the wedge. A lug on the right-hand side of 
the cocking lever extends toward the face of the wedge and serves 
as a latch to engage the hammer catch when the hammer is to be 
pulled back for percussion firing. When the cocking lever is in its 
normal position, the under edge of the latch lug rests on the face 
of the wedge and transmits to the wedge, instead of through the 
hammer and to the primer, any accidental blow upon the cocking 
lever. This precludes accidental firing which might occur were 
the cocking lever struck when the lock is closed. The hammer, 
mounted between the wedge and the cocking lever, is amply pro¬ 
tected from exterior blows. The slightest withdrawing of the 
wedge from the closed position removes the firing pin from the 
percussion cap of the primer and precludes firing electrically or 
percussively. The outer end of the wedge is so designed that it 
may he used in connection with the lock operator bars of any of 
the standard breech mechanisms. Lanyards are secured to the 
cocking lever by means of a hook. In addition to lanyard firing, 
the lock may he fired percussively in connection with hand- or 
foot-operated firing mechanisms incorporated with the various 
mounts by means of an extension which may he attached to the 
outer end of the cocking lever. 

479. The extractor is pivoted in the receiver and fits between 
the forward face of the wedge and the rear face of the mushroom 
stem. The extractor arms engage the primer shell on two sides, 
a clearance cut being provided in the extractor for the primer seat 
extension - on the rear end of the mushroom. The extension is 
added to the end of the mushroom stem to give better support to 
the primer. The extractor is actuated by an extractor cam which 
turns on the same pin as the extractor. When the wedge is 


Erf.ecu Mechanisms 


379 


retracted the lug- on the wedgo- face plate strikes the extractor 
cam, which, in turn, causes the extractor to swing to the rear, 
lifting the primer retaining catch out of the way and ejecting the 
primer. This extractor cam is also provided with a torsional 
extractor spring which returns it to the original position as soon 
as the wedge is sufficiently withdrawn. In priming, the primer is 
inserted between the arms of the extractor into primer seat. The 
head of the primer, seating in a recess cut in rear face of the 
extractor, pushes the extractor forward until the primer retaining 
catch engages the primer. The extractor and primer are pushed 
entirely home by the tapered cut on the inner end of the wedge. 

480. The primer-retaining catch consists of a catch housing 
which is secured to the upper end of the receiver by two screws, 
a catch which slides in and out of the housing, a guide screw which 
controls the outward movement of the catch, and a catch spring 
which keeps the catch in the correct retaining position. This catch 
sits in rear of the primer seat, and when the primer is inserted in 
the seat the catch is pushed in until the head of the primer is 
engaged by the forward face of the catch. \\ hen the wedge is 
closed and the primer is pushed home, the end of the wedge pushes 
the catch into its housing. When the primer is ejected, the arms 
of the extractor force the catch out of the way of primer. 

481. The lock-operator bar is secured to the carrier by meqns 
of a T-slot. The movement of the bar is controlled by a wedge 
operating plunger. The stop plunger is housed in the operating- 
bar. being held in the housing by means of a stop plunger key fitted 
in the forward face of the operator bar. a stop plunger spring 
being used to keep the plunger against the key. A stop plunger 
pull ring is attached to the end of plunger to enable the plunger to 
be lifted over the cam surface when withdrawing the bar from the 
carrier. This plunger works against a machined surface in the 
carrier and only allows the bar to be moved the distance necessary 
to close the wedge and to align the firing pin with the primer. 

482. The wedge-operating plunger is housed in the outer end 
of the operator bar, the end of the plunger entering the slot in 
the operating cam. This cam being secured to the operating handle 
of the breech mechanism causes the lock to open and close with 
the opening and closing of the breech mechanism. Lhe wedge 
operating plunger is secured in the housing by means of a wedge 


380 


Naval Ordnance 


operating plunger pin and plunger pin detent and is kept in the 
cam slot by means of a wedge operating plunger spring. Over 
the housing for the wedge operating plunger is secured the wedge 
hand operating lever. This lever has two helical slots diametrically 
opposite, through which it is secured to the housing by a plunger 
pin and by which, when the lever is pushed outward, the wedge 
operating plunger is lifted out of the cam slot. The operator bar 
can then be moved outward, withdrawing wedge. The wedge 
hand operating lever is used only for repriming or in assembling 
or disassembling the lock. The inner end of the operator bar is 
secured to the wedge by means of an operator bar pin with a 
spring detent. 

483. Safety appliances.—The primer cannot be fired either 
electrically or by percussion until the breech mechanism is com¬ 
pletely closed. The surface of the cam on the outer side of the cam 
slot is cut down to allow the wedge operating plunger to move 
over it in withdrawing the operator bar from the side. The surface 
of the cam on the inner side of the slide is too high for the plunger 
to slide over it, and as this surface follows the slot it prevents the 
operator bar (and wedge when fastened to the bar) from being 
closed until the breech mechanism is closed. A lug on the hammer 
engaging in a recess mill in the receiver lifts the hammer so as 
to break contact and prevent electric firing. This same lug also 
prevents the hammer from being drawn back for percussion firing, 
except when the wedge is fully closed. A pin is screwed into the 
carrier, fitting against the receiver, to prevent the lock from being 
turned in the wrong direction when disassembling or when dis¬ 
engaged from the operator bar. An arc plate is secured to face of 
carrier to preclude the possibility of the lock being turned until 
the wedge is retracted. It also prevents the wedge from being 
closed until the lock is in its proper position. If the pin locking 
the operator bar to the wedge is disengaged, by any means what¬ 
soever. the arc plate on the carrier automatically withdraws the 
wedge from firing position, thus preventing jamming and putting 
the wedge in the safe position so that the gun cannot be fired. 
When the receiver is in its correct position, with the wedge dis~ 
etigaged from the operator bar, and the breech mechanism is open, 
the wedge is prevented from being closed by a shoulder on the end 
of the cross-head bearing of the breech mechanism which will 
then be in front of the shoulder on the wedge. 


CHAPTER XI. PLATE IV 


REOEIVER- 
PRlMER- 


tFIRING POSITIONS 


PRIMER INSERTING POSITION 


ELECTRIC 


-WEDGE FACE PLATE 


P ERCU 55 ION 


HAMMER- 


COOKING LEVER. 



rl— MUSHROOM STEM 

o!ios * 



59523- I — RECEIVER 
59523-2-WEDGE 
S33 23 -3 - W EDGE FAC E P LAT E 
595Z 3 - 5 - EXT RACTOR 
59523- ©-EXTRACTOR PIN 
59523- 3-HAMMER GUIDE BLOCK:— 

53523- IO-HAMMER GUIDE BLOCK SCREW- 
53524- I-HAMMER 
59524 - 2-HAMMER THRUST PIN 

59524- <5-CONTACT PI EC EL _ 

7-CONTACT PIECE! INSULATION BUSHING 
-595 24- ©-CONTACT PIECE INSULATI ON WASHER 

9'HAMMERAND cocking lever, axle_ 

-595 24 - I o- TOR5ION WA5HER. 

5932-4— ' l— TORSION WASHER SCREW 

53524— I Z- COCKING LEVER.---_ 

59524 - \ 3 - 
12 2 - 3-4 1 - 


Cooking, LEVER SPRING 
SPRING COTTER PIN- 


-I 2-2- 3-40-SPRING COTTER PIN 
-59524- 3-HAMMER CATCH SPRING 

59524— 4- HAMMER CATCH- 

-59524- 5-HAMMER CATCH SCREW 
-59525- 1-FIRING PIN 


©-Z- 11 03- 3-TERM\N\AL NUT 

’ '°3-4«-TE^MlNAL stop nut 


-59525— 2-FlR|MG PIN NUT 

53525 A~ FIRING PIN INSULATION SLEEVE 


59525 <&—FIRING PIN BUSH ING- 

59525- 7 — FIRING pin SLEEVE 5PRIN( 
59525-8- FIRING SPRING 


- - - * ’ ~ —' ^ — —'— r • 

L S9525- 3~FIRING PIN INSULATION COLLAR 5 9 525- B-FFRlNG PIN SLEEVE 


FIRING LOCK, MARK XIV, MOD. I, NOMENCLATURE SHEET. 







































































































































































































































































































































































































Breech Mechanisms 


38i 

3-Inch Semi-Automatic Breech Mechanism, Mark V. 

(Plate V.) 

484. This mechanism, and the 3 -inch Mark IX, are the only 
3 -inch semi-automatic breech mechanisms used on U. S. Naval 
guns that are now in service. Both mechanisms are similar and 
are of the vertical sliding wedge type, which have been sometimes 
designated as the “ Driggs-Seabury semi-automatic mechanisms.” 
Several modifications have been made to remedy minor defects in 
the original design. 

485. The semi-automatic operation is as follows: 

When the gun recoils the tumbler crank on the left end of the 
crank shaft, H (Fig. 2 ) passes over the thrust cam, B (Fig. 8 ) 
forcing the latter down to the rear through 68 ° to 74 0 . After 
the tumbler crank has passed by the thrust cam, the thrust cam is 
released and returned to its original position by the thrust-cam 
spring (Fig. 5 ) so that on counter-recoil the tumbler lug brings 
up against the thrust cam (Fig. 9 ) and forces the crank shaft to 
rotate, thus causing the block to drop. As tht crank shaft is 
rotated the operating spring (Fig. 1 ) is compressed by means of 
the operating-spring piston and operating-chain stud on the right 
end of the crank shaft. As the block descends, the extractor lug 
C (Fig. 5 ) follows the extractor groove in the block, forcing the 
lower end of the extractor forward and the upper end to the rear, 
accomplishing extraction. The extractors are held to the rear 
while the breech is open by means of the extractor springs D 
(Fig. 4 ) and plungers, one to each extractor. 1 hese springs 
prevent the extractors from jarring forward upon the return of 
the gun to battery and causing premature closing of the breech. 
The block is held down by the inner lugs of the extractors, hearing- 
on shoulders (M, Fig. 4 ) in the block at the top of the extractor 
grooves. When the cartridge is loaded and brings up against the 
extractor nibs, the latter are forced forward and the extractor 
lugs aft, the extractor lugs becoming disengaged from the 
shoulders on the block. 1 he block is closed by means of the 
operating spring contained in a sleeve fitted on the right side of the 
gun. This spring is compressed on counter-recoil and remains in 
compression until the gun is again loaded. \\ hen a cartridge is 
loaded the extractor releases the plug and the operating spring 
closes the breech. 


Naval Ordnance 


382 

486. The cocking is accomplished as follows (see Fig. 4 ) : 

As the block rises the cocking lever toe E brings up against the 
sear nib. drawing back the firing pin and compressing the firing 
spring. The sear F fits into the left of the breech housing and is 
held in position by means of the sear spring plunger and sear 
spring T fitting into the left and rear of the breech. The sear is 
operated by the trigger bar which is operated by the trigger pull, 
acting through the trigger lever, trigger bar, head, and adjusting 
nut. When the trigger is pulled the sear is rotated against the 
force of the sear spring, the cocking lever is released by the sear 
nib and the firing pin flies forward. If the trigger were lashed 
back and the trigger bar in suitable adjustment, firing would 
result automatically as soon as the breech closes. 

487. The semi-automatic feature can be eliminated by turning 
the thrust cam B (Fig. 7 ) to the rear and down, thus permitting 
the tumbler crank on the crank shaft to pass above the cam as the 
gun returns to battery. For this purpose there is a tumbler latch 
1\ (Fig. 5 ) fitted in the tumbler cover which holds the thrust cam 
down and to the rear. The crank shaft rests in a cradle projec¬ 
tion under the gun and is held in place by means of a lock plate L 
(Figs. 4 and 5 ) fitted to the bottom of the breech housing by 
means of two dove tails and secured by means of the lock-plate pin. 
As the crank shaft is rotated the studded end of the breech-block- 
crank moves along a sloping cam surface on the under side of the 
block, raising or lowering it. The tumbler crank on the left side 
of the gun opens the breech on counter-recoil as previously 
explained. 

488. Operating lever clutch mechanism (Fig. 3 ). 

This mechanism is for the purpose of preventing rotation of 
the operating lever when the gun works semi-automatically. 

Where the operating lever is hollowed out to receive the end of 
the crank shaft, there is left a projecting sector of metal about 
1 inch thick. When the breech is closed and the operating lever 
is upright, the upper vertical face of this sector is against the 
corresponding face of the sector on the end of the crank shaft 
(Fig. 2 ). Consequently, rotation of the operating lever, when 
the breech is closed, will rotate the shaft, but rotation of the shaft 
will not rotate the lever since the shaft sector will move in a 
blank space. 


CHAPTER XI. PLATE V. 




Fig. 2.—Crank-Shaft. 



CKANK SHAFT SECTOR 
RETAINING RING 


OPERATING LEVER 

■CLUTCH 

;lutch string 

■CLUTCH LOCK 
BEARING 
■CLUTCH LOCK 



CLUTCH SECTOR 


l CRANK SHAFT 

SECTOR OF CLUTCH 

Fig. 3.—Clutch-Mechanism. 


rz/j 

l EDGE OF OPERATING 

LEVER SECTOR 


HOLE FOR DISMOUNTING TOOL 


TRIGGER SHAFT-a 


TR1GGER- 

PISTOL 
GRIP—I 


K* TUMBLER LATCH- 
TUMBLER COVER- 


THRUST CAM SPRING/ 



'PLUG OF EXTRACTOR SPRING 

Fig. 5.—Rear View. (Breech closed.) 


'EXTRACTOR PLUNGER-' LOCK PLATE- 
EXTRACTOR RECESS IN 

'EXTRACTOR PLUNGER SPRING GUN CHEEE “ 

LOCK PLATE LOCK BOLT cRMKsLt- 


TUMBLER CKANK 


Fig. 4.—Gun Gosed. (Breech closed.) 






3 -IN CPI S.-A. MECHANISM. MARK V. 
























































































































































































































































































Breech Mechanisms 


383 


By screwing in the clutch lock, the clutch is carried to the left 
against its spring and the sector on the left end of the clutch lock 
fills the space between the two other sectors, thus locking the shaft 
and operating lever together. When the gun is to function semi- 
automatically, the clutch lock should be screwed all the way out. 

5-Inch Breech Mechanism, Mark VII. 

(Plates VI. and VII.) 

489. Introductory.—The description in detail of the 5 -inch 
Mark VII breech mechanism follows: Except for minor details, 
this description covers also the 6 -inch Mark X, 8 -inch Mark \ I, 
12 -inch Mark IX, and 14 -inch Marks II, III, and IV breech 
mechanisms. 

In designing a carrier mechanism for turret guns, one of the 
most important difficulties to be overcome is to avoid slamming of 
the plug, which, due to its greater weight as compared with 
medium caliber mechanism, would necessarily bring severe strains 
upon the carrier and the operating mechanism. It is also desirable 
to avoid the use of gearing as much as possible, to reduce the 
number of parts and to transmit the power by means which reduce 
the friction to a minimum. 

In fitting the. firing mechanism, it is necessary, for safety, to 
prevent priming until the plug is locked, and to provide for easy 
repriming without danger to the personnel in the case of misfire. 

For overcoming the ill effects of the slamming of the plug as 
it swings into the screw box, it is possible to change the motion 
of translation of the plug into one rotation, thus cushioning the 
blow and utilizing the swinging energy of the plug to assist in 
locking it. This is done by means of a cam slot in the breech, 
and a follower pin on the plug. To avoid the use of gears, and 
still obtain the necessary power for unlocking, a crank shaft, 
with lever attached, is the most efficient device. To avoid the 
complication necessary to obtain a continuous motion of the 
operating lever to both rotate and swing the plug, it is found that 
the cam action which changes the swinging motion into lotating 
motion of the plug' also changes the direction of motion of the 
operating lever and permits of quick and easy operation of the 
plug, with the lever arranged to swing in two planes instead of 
one. This movement of the lever in a vertical plane aiound the 


384 


Naval Ordnance 


crank shaft for rotating the plug, and in a horizontal plane around 
the hinge pin for swinging it, results in several desirable features 
being obtained, as follows: 

1 . It eliminates the use of a carrier latch or a plug latch. 

2 . The operator stands entirely clear of the recoil. 

3 . When the plug is closed, the lever is in such position as to 
allow the plug man to catch it as the gun returns to battery and, 
by holding on to it, to have the forward movement of the gun 
unlock the mechanism. 

4 . It permits of a design of mechanism which does not require 
right or left hand parts. 

The speed of the mechanism depends entirely upon the dexterity 
of the operator, but it has been found that the plug can be opened 
or closed by an unskilled operator in two seconds with the gun 
level. Any greater speed is not recommended. It has also been 
found possible for one man to close the plug with the gun-elevated 
to an angle of 8 °. With one man on the operating lever and one 
man pushing on the plug, it has been found practicable to close the 
mechanism at any angle of elevation. 

The introduction of the rotating-cam slot and follower pin uses 
the energy stored up in the moving mass either to rotate the plug 
when closing or to swing out the mechanism when opening, and 
eliminates slamming and rebounding of the plug. It does away 
with the necessity of a closing buffer and the customary tray or 
carrier latch. 

Inefficient forms of power transmission, such as gears, racks 
and worms, have been eliminated, and bearings with large sur¬ 
faces have been introduced instead. A ball bearing on the upper 
hinge lug carries the dead weight of all swinging parts. 

The number of pieces has been greatly reduced. 

490. General design.—This breech mechanism is designed to 
fit the 5 -inch powder bag gun. The breech mechanism is of the 
carrier type, with the Welin breech plug, De Bange gas check- 
system and a new type of operating mechanism and firing 
mechanism. 

491. The carrier (see Plates VI and VII and Fig. 74 ) is 
journaled on a vertical hinge pin on the right hand side of the gun. 
The carrier extends across the breech face of the gun and has a 
projecting hub on which the breech plug is journaled. The operat- 


Breech Mechanisms 


385 


ing lever is attached to a shaft journaled in the carrier. The other 
end of this shaft carries an overhung crank, the pin of which 
en R a §T s a cross-head which works in a cross-head bearing set into 
the rear face of the breech plug. 

492. To open the mechanism, the operating lever is swung to 
the rear in a vertical plane. This rotates the crank shaft, which, 
by means of the cross-head, rotates and unlocks the plug. The 
operating lever is then swung to the side in a horizontal plane, 
which swings the carrier and plug clear of the breech. Reverse 
motions close the breech. A salvo-latch locks the operating lever 
in position so that it can only be unlocked by the recoil of the gun 
or by hand. 

493. Screw-box liner and breech plug.—The rear end of the 

gun jacket is threaded to receive the screw-box liner. The gas- 
ejector valve (not shown) is secured to the rear flange of the 
screw-box liner, and is opened when the breech plug is started to 
the rear in opening the breech. Air from the valve passes to 
two channels turned on the outside of the screw-box liner, and 
from these through ducts to the inner side of the screw-box 
liner and to the bore of the gun. 

The screw-box liner and the breech plug are slotted to form 
12 sections —4 blanks, and 8 threaded steps in four groups, the 
blanks being wider than the threaded steps to permit the action of 
the rotating cam. 

The breech plug is of the YYelin or stepped-screw type, having 
abutment threads with the pressure side the steeper. The center 
of the plug is bored out to provide a bearing for the mushroom 
stem and to receive the threaded hub of the carrier. This thread 
has the same pitch as the external thread on the plug. 

494. Mushroom and gas check.—The gas check system is of 
the De Bange type, consisting of a mushroom, gas-check pad, and 
gas-check rings (see Fig. 67 ). 

The stem of the mushroom extends to the rear through the 
breech plug and the hub on the carrier. The mushroom can move 
longitudinally, but is prevented from rotating by a key attached 
to the carrier. A helical spring located in a recess in the carrier 
and encircling the mushroom stem butts up against a nut on the 
same, and thus holds the mushroom in place. In rear of the nut, 
the mushroom stem has a bayonet joint for attaching the firing-lock 


CHAPTER XI. PLATE VI 



HINGE PIN 


GUIDE A 

STOP GUIDE 


.SALVO LATCH 


5-Inch Breech Mechanism—Side View. 





CHAPTER XI. PLATE VII 



5-Inch Breech Mechanism—Rear View. 


hinge, pin 


LOCK 








Naval Ordnance 


488 


receiver. The vent extends from the face of the mushroom 
through the stem, the end of which is bored out for the primer 
seat. 

495. Operating mechanism (Fig. 74 ).—The crankshaft, 
which extends through the carrier, is provided with two bearings. 
The inboard bearing engages the portion of the crank shaft 
adjacent to the overhung crank. 



Fig. 74.—Operating-Mechanism for 5-Inch Breech-Mechanism, 

Mark VII 


The outboard bearing for the crank shaft is machined in the 
shoulder of the carrier casting, which is bored out to fit a steel 
sleeve keyed to the crank shaft. To this sleeve is attached the 
operating lever and firing mechanism cam, these parts being keyed 
to the outer portion of the sleeve and clamped in position against 
a collar on the sleeve by the circular flange of a nut threaded on 
the extremity of the crank shaft and seated in a counterbore in the 
end of the cam. 


































































Breech Mechanisms 


3»9 


In the rear face of the plug, and located near the right hand 
edge, at an angular distance above the horizontal center line (un¬ 
locked) position equal to half the angle of rotation is a counter¬ 
bore into which is rigidly fitted a hollow, cylindrical cross-head 
bearing. The cross-head, which is housed in the cross-head bear¬ 
ing, engages the crank pin of the overhung crank, the parts being 
so arranged that the cross-head is capable of both a rotary and a 
sliding motion with respect to its bearing and crank pin. 

When the plug is closed and locked, as during firing, the operat¬ 
ing lever extends upward and toward the muzzle, making an angle 
of 43 0 with the vertical. The cross-head and bearing are below the 
horizontal center line at an angular distance of 16 0 42 ' 30 " (equal 
to half the rotation of the plug) and the crank shaft is in the dead 
center position, with the crank pin directly in line with the center 
of the shaft when viewed in the plane of rotation of the plug. 
The plug is thus securely locked against any rotary tendency pro¬ 
duced by reason of the chamber pressure and the inclination of the 
plug threads. 

496. To open the breech, the operating lever is moved to the 
rear until it reaches the horizontal position, turning the crank 
shaft through an angle of 133 0 . The corresponding circular 
motion of the crank pin is resolved by the cross-head within its 
bearings and an upward movement of this bearing, which, being 
rigidly attached to the plug, causes a rotation of this member in 
the direction required to disengage the threaded steps. At the 
beginning of this motion, as the crank pin leaves the dead center 
position a large angular movement of the lever and crank shaft 
will produce but a snjall rotation of the plug, with a corresponding 
increase in the force available to unseat the gas-check pad. 

497. Plug-rotating cam.—The total angular movement of the 
plug produced by the rotation of the crank shaft is 33 ° -5'y 
which movement but 26 ° 42 ' 5 " is required to disengage the 
threads, the remainder of the rotation occurring as the carrier 
begins to swing away from the gun, thus affording an easy transi¬ 
tion from the rotary motion of unlocking the plug to the trans- 
latory motion of swinging it out of the breech. I his effect is 
accomplished by the plug-rotating cam, which is fitted in a dovetail 
in the blank between the threaded sections on the left side of the 
screw box, and consists of a hardened-steel plate into which is cut 


Naval Ordnance 


390 


a curved cam-slot coinciding' in its forward portion with the 
pitch of the screw-box threads, and running' out at the breech face 
in the path of the parts swinging about the hinge pin. This cam 
slot engages a stud or can, follower projecting from the side of 
the breech plug, and guides it during the latter part of the motion 
of unlocking, so that, as soon as the threads of the plug are dis¬ 
engaged, the rear-ward motion of the plug and carrier, in swinging 
about the hinge pin, is gradually started without the shock to the 
mechanism or to the operator which would result were the direc¬ 
tion of motion changed suddenly. The advantages derived from 
the use of the plug-rotating cam are most marked during the act 
of closing the breech, when, by checking gradually the velocity of 
the swinging parts, it serves to avoid the objectionable slamming 
and rebounding of the carrier by utilizing and absorbing the energy 
of the swinging parts in imparting a rotary motion to the plug and 
operating lever. 

498. Operating-lever guide and stop (see Plate VI).—The 
rearward swing of the carrier about the hinge pin, commenced by 
the plug-rotating cam. is continued by the operating lever until 
the mechanism lias been swung through 90 °, when further swing 
is limited by recessed stops on either side of the carrier hinge, 
which come up against corresponding abutments formed upon the 
hinge Jug forging. While the mechanism is open, the plug is 
prevented from rotating and is maintained in the unlocked position 
by the operating lever guide, a projection from the hub of the 
operating lever, which, as the outward movement of the mechanism 
about the hinge pin commences, enters a guide slot in the hinge- 
lug forging. This device and the rotating cjim prevent the plug 
from rotating while the threads of the plug and screw box are 
disengaged. 

To guard against the failure of the guide on the operating 
lever hub to enter fairly the guide slot, which might occur if lost 
motion should develop in the operating gear, an operating lever 
stop is provided to limit the rotation of the lever and crank shaft. 
This stop consists of a pin driven through the hub of the operating 
lever, and which is provided with a stud projecting inwardly to 
engage a slot milled in the outboard end of the carrier (not 
shown). 


Breech Mechanisms 


39 1 


499 . Operating-lever latch (salvo latch) (Plate VI).— I he 
lever latch consists of a latch member journaled on a screw bolt 
attached to the forward edge of the hinge lug in line with the 
operating lever guide slot. A locking plunger is mounted in a 
recess directly in the rear of the latch boss, and in such a position 
that the plunger is retained in place by an overlapping portion of 
the latch. The upper portion of the latch is broad and heavy, and 
is machined at its upper extremity to engage the hook or catch 
formed on and projecting from the under side of the opeiating 
lever. The lower part of the latch is made as light as possible, 
and is bored out to provided a bearing for the latch-spring and 
plunger, which, by acting against the hinge lug. throw the latch 
into proper position to engage the catch on the operating level. 

During recoil, the inertia of the upper and heavier parts of the 
latch causes it to rotate on its pivot so that the lower portion moves 
to the rear toward the hinge lug. compressing the latch spring, and 
the upper portion moves forward and out of engagement with 
the catch on the operating lever. 1 he latch is held in this i eleased 
position by the locking plunger, which, under the impulse of the 
locking plunger spring, moves out and engages a notch in the latch 
as soon as it is brought into line by the rotation of the latch. \\ hen 
the breech is opened the lug on the operating lever strikes the lock¬ 
ing plunger, compressing its spring, and moves the projecting stud 
out of engagement with the notch in the latch, which thereupon, 
under the action of the latch spring and plunger, is returned to 
the “ set ” position ready to engage the catch on the operating 
lever when the breech is closed. 1 he top part of the latch selves 
as a stop which comes up against the hinge lug and limits the 
rotation of the latch. 

As the latch does not release automatically except upon the dis¬ 
charge and recoil of the gun, it gives warning of misfires, or hang 
fires, which might pass unnoticed when a number of guns are 
being fired in salvo. In such case, the breech can only be opened 

after releasing the latch by hand. 

500. Firing mechanism.—This breech mechanism is fitted with 

the Mark XIV Mod. I firing lock previously described. 


CHAPTER XI. PLATE VilJ 



14-Inch Breech Mechanism, Mark III, Modification I, 
Plug Open—Side View. 








CHAPTER XI. PLATE IX 



AIR LINE TOCLOSING 
Cylinder 


REALANCf. SPRING 


COUNTERBALANCE AND CLOSING cylinder 


14-Inch Breech Mechanism, Mark III, Modification I. 
. Plug Closed—Site View. 



394 


Naval Ordnance 


14-Inch Breech Mechanism. 

(Plates VIII, IX and X.) 

501. General design.—The 14 -inch Mark 111 Mod. I breech 
mechanism is similar to the 5 -inch Mark VII (Naval Gun Factory 
design). The principal features in which this mechanism differs 
from the breech mechanisms of the same type on other guns are 
enumerated below. 

This breech mechanism is adapted to guns mounted in three- 
gun turrets, by turning it through 90 °, so that the carrier opens 
downward. The operations of opening and closing the breech 
mechanism are facilitated by the introduction of a counter-balance 
spring and a closing cylinder operated with compressed air. 

The carrier is provided with trunnions which are journaled in 
hinge lugs, fitted in recesses cut in the front side of the flange on 
the screw-box liner. The hinge lugs are screwed in place by 
body-fit bolts. The carrier extends upward across the breech face 
to the center of the gun, where it has a projecting journal which 
carries the breech plug. The operating lever is attached to the 
lower end of a vertical shaft which is journaled in the carrier near 
the center line. The upper end of this shaft carries an overhung 
crank, the pin of which engages>a cross-head which works in a 
cross-head bearing, set in the rear face of the breech plug. 

502. To open the mechanism the operating lever is swung to 
the rear and left either by hand or by means of a lanyard. This 
rotates the crank shaft, which, by means of the cross-head, rotates 
and unlocks the plug. I he mechanism is then swung open to the 
rear and downward by means of the plug handle and its own 
weight. V hen open, the mechanism is supported by the counter¬ 
balance spring, which also serves as a buffer. 

A\ hen the valve which admits compressed air to the closing 
cylinder is opened, the air pressure on the piston closes the 
mechanism. I his air is taken from the gas ejector system, and 
before reaching the inlet valve passes through a reducing valve 
which maintains a constant pressure independent of the fluctua¬ 
tions in the air line. 1 he operating lever is locked in the closed 
position by the salvo latch, and is unlocked b\ r the recoil of the 
gun or by releasing the salvo latch by hand. 

503. Control arc and stops.—The rearward swing of the 
carrier about the hinge pin. commenced by the plug-rotating cam. 
ls U)n tinued by means of the plug handle until the mechanism has 
swung through an angle of 90 °, when further swing is limited by 


chapter xi. plate x 



FIRING 

LOCK 


CARR IER 


COUNTERBALANCE SPRING 

OPERATING lever 


14-Inch Breech Mechanism, Mark TV, Modification I 






Naval Ordnance 


396 

the counter balance and a stop. While the mechanism is open 
the plug is prevented from rotating in the closing direction by 
the control arc engaging the adjacent high section of the plug 
(see Plate VIII). The control arc is a circular steel segment, 
concentric with the hinge, and is bolted to the screw-box liner 
between the hinge lugs. 

504. The counterbalance and closing cylinder (Plate IX) is 
supported by the closing cylinder bracket, which is pivoted in a 
journal under the recoil cylinder lug of the yoke. The spring-rod 
piston, which works in the closing cylinder, is extended upward 
and to the rear by the spring rod. The spring rod terminates in a 
head with an offset hook which bears on a pin in the carrier cam 
bracket. The cam bracket is bolted to the left hand hinge pin boss 
of the carrier. The counter-balance spring surrounds the spring 
rod, and extends from under the head of the latter to the spring 
adjusting nut which is screwed on the outside of the closing 
cylinder. By means of this nut. the tension of the spring is ad¬ 
justed. The body of the valve for admitting compressed air to the 
closing cylinder serves as a cylinder head. The valve plug is 
operated by the valve handle located on top of the spring rod head 
and connected to the plug by the telescoping valve shaft and sleeve 
passing through the center of the spring rod. Compressed air is 
led to the valve through a ^-inch pipe and flexible hose from the 
air supply system. 

The power of the spring and its lever arm are so designed that 
during the opening of the breech mechanism this is nearly balanced 
until fully opened, when an extension on the carrier bracket is 
brought in contact with the head of the spring rod, suddenly 
increasing the lever arm of the spring, which is thus enabled to 
take the shock and stop further motion of the mechanism. 

505. To close the breech mechanism, compressed air is 
admitted to the closing cylinder by opening the valve by hand. 
Fhe air pressure on the piston is transmitted through the spring 
rod to the carrier cam bracket. When the mechanism is nearly 
closed, the ball on the closing rod comes in contact with the valve 
closing rod pin, automatically revolving the valve shaft and closing 
the valve, and at the same time opening a by-pass from the closing 
cylinder to the atmosphere. 

The firing mechanism consists of firing lock Mark XIV Mod. 1 
which has been previously described. 


CHAPTER XII. 

NAVAL GUN SIGHTS.* 

Preliminary Definitions. 

506. (i) The axis of the bore of the gun is its longitudinal 
geometrical axis. 

( 2 ) The axis of training of a gun is the axis of motion of the 
top carriage in azimuth; this axis must be installed so that, when 
the ship is on an even keel and normally trimmed, it will be per¬ 
pendicular to the plane of the horizon. 

( 3 ) The axis of the trunnions is their common geometrical 
axis; the side must be so machined that this axis will be accu¬ 
rately at right angles with the axis of bore. The adjustment of 
the frictionless trunnions (or, in the case of small guns, the 
machining of the trunnion seats) must be such that the axis of 
trunnions is accurately at right angles with the axis of training. 
Then, when the ship is on an even keel and normally trimmed, 
the axis of the bore will move in a plane vertical to the plane of 
the horizon when the gun is moved in elevation. 

( 4 ) A modern naval sight mount is a mechanism, attached to 
or connected to the gun slide, that carries two points, called the 
front and rear sight points, whose positions relative to each other 
are rigidly fixed. In Plate I, the front sight point S is the apex 
of a cone ; the rear sight point S is the bottom point of a V-shaped 
notch; the straight line prolonged through these two points is 
called the line of sight. 

( 3 ) The trajectory is the curve described by a projectile in 
passing from the muzzle of a gun to the point of impact; its 

* Rear Admiral Bradley A. Fiske, U. S. N., invented the application of the 
telescope-sight as a permanent part of the gun-mount, in 1892; prior to this 
telescopes had been used, but they were always removed from the gun 
before firing. 

The development of the telescope as a night-sight was the result of origi¬ 
nal experiments that were made by Lieutenant Commander H. C. Mustin, 
U. S. N., while on duty at the Gun Factory iri August, 1905- He also 
designed telescopes Marks XI, XII and XIII (prismatic) in 1905-1906. 
The other inventions of his referred to in the text are as follows: Periscope 
sight-mount for turret-guns, in 1904; periscope sight-mount for broadside 
guns, in 1906; focusing-cap, in 1906. 

397 


398 


Naval Ordnance 


downward curvature Mud (Fig. 75 elevation) is due to the force 
of gravity; its lateral curvature Mml (Fig. 75, plan) is due to the 
rotation of the projectile that is imparted by the rifling of the 
gun. This deviation from the vertical plane of fire is called the 
drift, and is to the right in all our guns. 

(6) The line of departure is the tangent to the trajectory at 
the muzzle of the gun; it is coincident with the axis of bore at the 
instant the projectile leaves the gun (MM', Fig. 75.) 

(7) The jump is the small vertical angle, usually upward, 
which the axis of the bore describes in the act of tiring (j, Fig. 75) ; 





Axis of Trunnions 



it is due to a yielding in the supports of the gun, caused by the 
shock of discharge. 

(8) The angle of position for a given target is the vertical 
angle between the plane of the horizon and the line of sight, when 
the line of sight passes through that target (p, Fig. 75 ). 

(9) The angle of elevation is the vertical angle that the line of 
sight makes with the plane through axis of the bore and axis of 
the trunnions (6, Fig. 75). 

(10) The angle of departure is the vertical angle between the 
line of departure and the plane of the horizon («. Fig. 75). When 
the jump and angle of position are negligible, as they are assumed 












CHAPTER XII. PLATE I 



-Plan 


L i h e_o f S'tj A f“ 


Axis w' Should Intersect Axis hh'. 














































400 


Xaval Ordnance 


to be in naval gunnery, the angle of departure is the same as the 
angle of elevation. 

(12) The angle of fall is the vertical angle that the tangent to 
the trajectory at the point of fall makes with the plane of the 
horizon (oj, Fig. 75). 

(13) The range is the distance in a straight line from the gun 
to the ‘ point of fall.” When the point of fall is in the same hori¬ 
zontal plane as the gun, the range is called the “ horizontal range.” 
Ordinarily the word “ range ” is used to designate the “ horizontal 
range.” 

The word “ range ” is also used aboard ship to designate the 
“ range-finder range ” which is almost never the same as the actual 
” range.” Another use of the word is to signify the “ sight-bar 


range. 


The loose usage of this word is to be deplored, and unless it is 
definitely stated what usage is meant it is only from the context 
of the subject that it can be determined whether the true “ hori¬ 
zontal range,” the “ range-finder range,” or the “ sight-bar range ” 
is intended. In actual practice these three ranges are never all 
the same in numerical value, though fairly close together. 

(14) The danger space is the distance through which a target 
of a given height can be moved from the “ point of fall ” directly 
toward the gun and still have the projectile pass through the target. 

If the “ maximum ordinate,” or highest point of the trajectory, 
does not exceed the height of the target the “ danger-space ” is 
evidently equal to the range, and such a range is known as the 
“ danger range/’ 

If h be the height of the target in feet, an approximate value for 
the “ danger space ” is given by the expression 


d — U cot <0. 


If the target has a beam k feet the approximate danger space 
will be 


d = k + h cot w. 


A more exact formula for the danger space is given by the 
expression 



where X is the range in feet. 

(15) The virtual height of a target is equal to d tan w approx. 




Naval Gun Sights 


401 


Fundamental Requirements. 

507 . All sights must fulfil the following fundamental require¬ 
ments : 

(a) To set the line of sight at any specified angle with the 

plane through axis of bore and axis of trunnions; for this pur¬ 

pose there is required the horizontal sight axis hh', which neces¬ 
sarily must be installed exactly parallel to the axis of trunnions. 

(b) To set the line of sight at any specified angle with the 

plane through the axis of bore that is perpendicular to the axis 

of trunnions; for this purpose there is required the vertical sight 
axis w', which must be installed exactly at right angles with the 
axis of trunnions. 

The fundamental requirements of a sight-mount are illustrated 
in Plate I; every modern naval sight, whatever its type may be, is 
based on principles shown in this figure. The bar which carries 
the front and rear sight points, S' and S, is called the pivot bar. 

To meet the first requirement of the mechanism, the pivot block 
p. to which the front end of the pivot bar is attached, engages the 
shaft whose axis hh' is the horizontal sight axis installed exactly 
parallel to the axis of the trunnions. Vertical motion is imparted 
to the pivot bar and to the line of sight by raising the curved bar 
IV, called the sight bar; this moves in the casing C, called the 
sight-bar bracket, which has a fixed position relative to the bear¬ 
ings of the horizontal sight axis. The front and rear faces of the 
sight bar, and the interior front and rear faces of the sight-bar 
bracket, are machined to arcs of circles centered in the horizontal 
sight axis. It is evident that the side faces of the sight bar and 
the interior side faces of the sight-bar bracket must be in planes 
perpendicular to the horizontal sight axis; otherwise, vertical 
motion of the sight bar would cause an appreciable lateral motion 
of the rear sight point, and a consequent deviation in the lateral 
setting of the line of sight. 

To meet the second requirement of the mechanism, the pivot 
bar engages a pin in the pivot block whose axis is vv', installed 
exactly at right angles to the horizontal sight axis hh' and inter¬ 
secting it. Lateral motion is imparted to the pivot bar and to the 
line of sight by moving the rear end of the pivot bar in a groove 
in the azimuth head; the front and rear faces of this groove and its 
fitting on the rear end of the pivot bar are machined to arcs of 


27 


402 


Naval Ordnance 


circles centered in the vertical sight axis. It is evident that the 
flat contiguous faces of these parts must be in planes parallel to 
the horizontal sight axis and at right angles with the vertical sight 
axis; otherwise lateral motion of the sight bar would cause an 
appreciable vertical motion of the rear sight point and a consequent 
deviation in the vertical setting of the line of sight. 

The means of imparting motion to the pivot bar are. for the sake 
of simplicity in the drawings, omitted from Fig. i and the follow¬ 
ing illustrations of sight mounts. They are as follows: Vertical 
motion is given by a worm wheel, journaled in the sight-bar 
bracket, that engages a worm on the rear face of the sight bar; 
the worm wheel is connected by miter gears to a hand wheel which 
has a small crank handle. Lateral motion to the pivot bar is given 
by a worm wheel on the azimuth head that engages a worm on the 
rear end of the pivot bar; the hand wheel for lateral motion is 
similar to the hand wheel for vertical motion. 

Sight Scales. 

508 . There are two kinds of scales on every sight. One kind 
indicates the movement of the line of sight about the horizontal 
sight axis ; this is called the range scale. • The other kind is for indi¬ 
cating the movement of the line of sight about the vertical axis, 
and is called a deflection scale. Sight scales are either direct read¬ 
ing or multiplying; the direct reading type will be described first. 

509 . A direct-reading range scale suitable for the sight mount 
in Plate I is shown in Fig. 76. The range strip, made of white 
metal, is engraved with the divisions and numbers of the scale; it 
is dovetailed to fit in the sight bar flush with the outer side face, 
and is adjustable within the limits of the elongated hole for the 
clamp-screw E. The arc of a circle Y (shown in broken lines), 
which touches the rear ends of the scale divisions and front eiid of 
K, the reference mark on the sight-bar bracket, is centered in the 
horizontal sight-axis hh' Plate 1 . This circle gives a basis for lay¬ 
ing off the spacing of the scale divisions, wdiich are calculated 
from data obtained at the proof firing of the gun. The divisions 
read in yards of range for certain standard conditions as follows: 

(a) Atmosphere of unit density. 

(b) Powder charge of a certain weight and index that, at a 
temperature of 90° F.. will give a muzzle velocity of a certain 
number of foot-seconds. 


Naval Gun Sights 


403 


(c) Projectile of a specified weight and coefficient of form. 

(d) Force of wind on the range zero. 

For the above conditions, the angle of elevation for every range 
from 100 yards up to that which will be given by an elevation of 
15 0 is computed and laid ofif on the arc Y, measuring from the 



\ 

\ 

\ 

4 

Fig. 76. 

zero mark. For instance, under standard conditions, it is deter¬ 
mined that a range of 5000 yards requires an angle of elevation 
of 5 0 40'; then an arc of 5 0 40', measuring from the zero division, 
is laid ofif, and the division numbered 5 000 1S plotted. 















404 


Naval Ordnance 


Adjustments of the zero divisions are two of the details of bore 
sighting —a subject which is described more fully in paragraph 
543. A bore sight consists essentially of two sight points placed 
accurately coincident with the axis of the bore; by means of these 
and the elevating and training gears of the gun. we can lay the 
axis of bore on a certain mark which is at a mean target practice or 
battle range; then, by motion of the pivot bar we can direct the 
line of sight to the same mark (Fig. 77). 

At present we are interested only in the range scale; this must 
now be shifted to read zero by shifting the position of the range 
strip or, as is arranged for in some sight mounts, by shifting the 
reference mark. After this is done, the gun is said to be bore- 
sighted in range for the mean range selected. Say this is 5 000 






Lint 




S_ 5 * /!<»« e f 

H-» —Z^D- 


^ ft x i 3 of B»r« 

Fig. 77. 


E (f U ~t <■ ' O M 


yards. Now if we raise the sight bar to the reading 5000, and 
move the elevating gear of the gun until the line of sight is 
directed to the target, the gun will be at the proper elevation to 
give a range of 5000 yards under the standard conditions (a), (b). 
(c), and (d). Now if the gun is fired under these conditions, 
from a motionless ship at a motionless target, the projectile will 
attain a range of 5000 yards; but it will fall to the right of the 
target an amount D (Fig. 75), which is the drift corresponding to 
5000 yards range. 

In the above example we bore sighted for a mean range of 5000 
yards; it is therefore evident that there will be a small vertical 
pointing error, when we fire at other ranges, unless we have a 
sight-mount that has its horizontal sight-axis coincident with the 
axis of the trunnions. For instance, if the horizontal sight axis is 







Naval Gun Sights 


405 

5 feet higher than the axis of the trunnions—as it is in some turret 
sight mounts—and we have bore sighted for a mean range of 5000 
yards, we shall have a pointing error 2\ feet low when firing at a 
range of 2500 yards, or we shall have a pointing error of 2 \ feet 
high at a range of 7500 yards. But we are better off than if we had 
bore sighted by the old method of pointing at a star, and thereby 
adjusting the line of sight parallel to the axis of bore; this, in 
the above example, would give us a pointing error of 5 feet low 
at all ranges. 

510 . Drift compensation.—The lateral error D, in Fig. 75, due 
to the drift at a range R, represents an angular error, which is 

practically tan' 1 ^. To compensate this, we move the rear end of 

the pivot bar to the left through an angle tan -1 — ; then train the 
gun to the left until the line of sight is again directed to the target 



T, as shown in Fig. 78. The next shot will be a hit, provided we 
have the standard conditions (a), (b), (c), and (d), above. 

511 . A deflection scale is used primarily for making the drift 
compensation ; a direct-reading deflection scale with its mounting, 
suitable for the sight mount shown in Plate I is shown in Fig. 79. 

The pointer P is attached to the rear end of the pivot bar by 
the screws a and b, and is adjustable vertically, with reference to 
the pivot bar, within the limits of the elongated holes for these 
screws. The rear surface of the azimuth plate is machined to the 
surface of the toroid that is generated by the lower end of the 
pointer P when the pivot bar is moved about its two axes; this 
plate is dovetailed into the sight-bar bracket, and is adjustable 
horizontally within the limits of the elongated holes for the clamp- 
screws c and d. 

In bore-sighting the gun, after the range strip has been shifted 
to read zero, the next step is to make the deflection scale read zero. 






406 


Naval Ordnance 


First, raise or lower the pointer P, with reference to the pivot bar, 
until the lower end of the reference mark is on the level of the zero 
mark on the azimuth plate; then shift the azimuth plate to the 
right or left until the center of the zero mark is at the lower end of 
the reference mark. Fig. 79 shows the sight bar raised to the 
reading 1000 yards after range- and deflection-scale adjustments 
have been made; the lower end of the reference mark is now 



at the position p; its position for ranges 2000, 3000, 4000. 5000 
would he q, r, s, t, respectively, if no lateral motion is given to the 
pivot bar. Now, if we move the rear end of the pivot bar to the 

left from the position p through an arc pp,= tan -1 — tt a t 1000 A 

■ 1000 

to the position />,, we shall have compensated the drift at 1000 
yards range as in Fig. 78. Similarly, we can locate the points p.,, 
Ps> Pa* Pa, etc., by laying ofif the arcs, qp 2 , rp s , sp t , tp 5 , etc., which 
correspond respectively to the drift at ranges 2000, 3000, 4000, 

























































Naval Gun Sights 


40 / 


5000, etc., and can lay down a fair curve through the zero mark 
and the points p x , p.,, p. it p 4 , p., etc. When the sight bar is raised 
to any range reading and the pivot bar is moved to the left until 
the reference mark on the pointer touches this curve, a shot fired 
under the standard conditions (a), (b), (c), and (d), Art. 509, 
will have no drift error. This curve was formerly called the zero 
line, but now, for convenience in sight setting (as will appear 
later), it is called the fifty line and is numbered as in Fig. 79. 

512 . Speed compensation.—Thus far we have considered the 
ship and target motionless, but. in naval gunnery, either the target 
or ship or both are steaming ahead. We will examine the case of 
firing from a stationary ship at a target steaming at a speed of 
k knots per hour on a course at right angles to its bearing; we 
assume that there is no breeze, and that we have standard con¬ 
ditions in the atmosphere and ammunition. 



In Fig. 78, SS'T is the line of sight, MmT is the trajectory, R 
is the range; the sight has been set in azimuth with deflection 
pointer touching the fifty line, so the drift is compensated. T is 
the position of the target at the instant of firing, and t is the time 
of flight of the projectile for the range R. The shot will fall to 
the right of the target; for, during the time of flight, the target 
has moved to the piston V. The lateral error is TT' = kt , and 


the angular error is tarr 1 -J.. To correct this error we move the 

A 

pivot bar to the left through an angle tan -1 ^, which gives the 


condition shown in Fig. 80. 

in the above example, we will assume the range is 1000 yards, 
the time of flight is and the speed of the target is two knots 
per hour. Then, laying ofif on the azimuth plate in Fig. 79, the 





408 


Naval Ordnance 


arc tan -1 ——we locate the point jl ; when the pivot 

IOOO 

bar is moved to the left so that the reference mark on the deflec¬ 
tion pointer is at the position n lf the sight will be set for com¬ 
pensating the speed of two knots in the example given. Similarly, 
for ranges 2000, 3000, 4000, etc., and corresponding times of 
flight to, t z , t 4 , t z , etc., we locate the points n 2 , » 3 , n 4 , n 5 , etc., and 
can lay down a fair curve through these points and n x ; then, when 
the sight bar is raised to any range and the pivot bar is moved to 
the left until the reference mark touches this curve, the error due 
to two knots speed will be compensated when the target is moving 
in the direction shown in Fig. 80. The curve for compensating 
two knots speed when the course of the target is in the opposite 
direction, is plotted by laying oft" arcs equal to p 1 tt 1 , p 2 n 2 , /> 3 « 3 , 
Pi n 4> Ps n 5> etc., to th e right, instead of to the left, of the fifty line. 
The other speed lines shown in Fig. 79 are computed in the same 
manner, using the proper values of speed, range, and correspond¬ 
ing times of flight. The method of numbering the lines shown in 
this figure obviates the use of the words “ right ” and “ left ” in 
designating the setting of the sight in azimuth. This avoids the 
errors that formerly were frequent on account of confusing right 
with left; it also simplifies the visual fire-control instrument, 
because the indication for the azimuth setting requires only two 
numerals, instead of two numerals and the designation “ right ” 
or “ left.” 

513 . Sight radius.—The length from the center of the vertical 
pivot, V, Plate I, and Fig. 99, to the center line of the “ azimuth 
head,” or the distance between the front and rear sights in open 
sights as in Figs. 86 and qo is called the “ sight radius.'’ Knowing 
the sight radius, we are able to obtain definite values for these arcs 
by spacing oft" the distances between the drift curves on the 
azimuth plate (Fig. 79). 

Assume that we are firing a 12-inch gun having an initial 
velocity of 2900 foot-seconds at a target 1000 yards distant and 
moving at two knots speed (3.38 foot-seconds). By referring to 
the 12-inch 2900 foot-seconds range table (column 4), we find 
that for a range of 1000 yards the time of flight is 1.05 seconds. 
Let the sight radius of the gun equal B inches, and let x equal the 
length in inches to lay off on the azimuth plate to compensate for 
the speed of the target. 


Naval Gun Sights 


409 

3.38 feet X 1.05 (time of flight) =3.549 feet, the distance the 
target will steam at 2 knots in the time of flight of the projectile. 
Then from similar triangles, considering OT — OT' and OS = 0 S', 

B : R=x: D, 

B in inches : 3000 = *: 3.549, 

3 - 549 # 

3000 * 

Let us give B a value of, say, 100 inches. Then # = .118-l-inch. 



By the same method for 3000 yards range, we find x— .123 inch ; 
for 5000 yards range, x— .127 + inch. Working it out for longer 
ranges, we get gradually increasing lengths of x, which illustrates 
why the drift curves are close together at the bottom of the azi¬ 
muth plate and wider apart at the top. 

514 . Azimuth plates are marked in knots for speed of target. 
This is obviously the right method, as will be seen. Let us try to 
mark the azimuth plate for speed of ship, the target being sta¬ 
tionary. Assume the ship steaming ahead at 2 knots speed, firing 



at the target T. The speed of the ship will give to the projectile a 
component in the direction of motion of the ship equal to 2 knots 
per hour, which, if the firing were in vacuum, would cause the pro¬ 
jectile to fall at A, and AT-Oa', the distance the ship would steam 
in the time of flight. However, we are not firing in vacuum, but 
in still air, and the projectile would be driven to the right by an 
apparent wind of 2 knots per hour, which would begin to act as 
soon as the projectile left the gun, and its effect would increase 
with the range. Therefore the projectile would fall at B. 
(Fig. 82.) 





4 io 


Naval Ordnance 


Referring to the 12-inch range table, we find that for a range of 
1000 yards the effect of the apparent wind on a 12-inch shell would 
be practically negligible: the firing ship would advance 1^ yards, 
and the shell would be deflected to the left i-J yards. (As a matter 
of fact, the shell would feel the effect of the apparent wind; but at 
this short range we can neglect it.) At 5000 yards range the 
firing vessel would advance 6^ yards; the shell would miss the 
target by 5^ yards. The difference, f yard, is the effect of the 
apparent wind on the shell during the time of flight. At 10,000 
yards range the firing ship would advance 14 yards; the shell 
would miss the target by nf yards. The difference, 2\ yards, is 
the effect of the apparent wind during the time of flight. In every 
case, in order to know the number of yards to be allowed for speed 
of ship, we should necessarily take into account the effect of the 
apparent wind, which varies with the strength of the wind and the 
time of flight. The target, however, during this time of flight, 
steams a certain definite distance which is dependent on no other 
elements. It is thus much simpler to mark the azimuth plate for 
speed of target than to mark it for speed of ship. 

If the target is speeding at 10 knots at right angles to the line 
of fire, we set the deflection scale at 50 ± 10, to compensate for the 
speed of the target. If the target is anchored and the firing ship 
is steaming at 10 knots speed at right angles to the line of fire, 
the setting of the deflection scale would be 50 ± (10 —effect of the 
apparent wind). This can be readily obtained from the range 
tables. 

515 . Azimuth errors.—The speed curves on the deflection scale 
shown in Fig. 79 are accurate only under the following circum¬ 
stances: (a) When there is no breeze on the range, (b) when we 
have standard conditions in ammunition and atmosphere, and (c) 
when we fire from a stationary ship at a target steaming on a 
course at k knots per hour at right angles to its bearing. 

The error that arises if the deflection scale be set for the full 
speed of the target when the course of the latter is at an angle 
C with its line of bearing is shown in Figs. 83 and 84. In these 
figures R is the range at the instant of firing; t is the time of flight 
for that range; T is the position of the target at the instant of 
firing; T' is its position at the instant of impact. It should be 
noted in both figures that an error in range as well as an azimuth 


Xavai. Gun Sights 


411 

error is introduced. In both cases the sight is over compensated in 
azimuth. 

In the first case the target is steaming partly with the direction 
of motion of the projectile, and in the second case partly in the 
opposite direction. Since the distance the target steams in the 
time of flight is small in comparison with R, we can say without 
much error that there has been no change in range. But since we 
are now dealing only with azimuth errors, we are interested in 



Error c/7 JJef/ecf/a/7. 




obtaining the component of the target’s speed at right angles to the 
line of bearing, in order to know the azimuth setting. In both 
cases it is T'N, which is equal to k cos C; and the setting of the 
deflection scale should be 50 cos C- 

IVhen both ship and target are moving .—Let us assume the 
firing ship S (Fig. 85) is steaming at 10 knots on course North, 
and the target ship T 10 knots on course South, and that at com¬ 
mencement of firing with 12-inch guns the target ship bears 60 










412 


Naval Ordnance 


on the starboard bow of the firing ship. The combination setting 
is the algebraic sum of the compensation for speed and course of 
the target and for speed and course of the firing ship. If there is 
no breeze, that part of the setting involving speed and course of 
the firing ship will be in error by reason of the effect of the appar¬ 
ent wind component. If there is a breeze, both parts of the com¬ 
pensation may be in error. The setting of the deflection scale 
will be: 

Due to target ship: 50+ 10 sin 6o° = 58.7 
Due to firing ship: 50+ 10 sin 6o° = 58.7 

Therefore, if the deflection scale is set at 504-17.4 = 67.4 the com¬ 
pensation is made; but it is in error because we have neglected this 
effect of the wind component on the shell. 

To get the true azimuth setting we would proceed as follows: 
Referring to the 12-inch 2900 foot-seconds range tables, 5000 
yards range. 

Due to target ship: 

8 7 

Lateral deviation to left of target,X38 (col. 18) =27.6 yards. 

Due to firing ship: 

8 7 

Lateral deviation to left of target,LyX35 ( co l. 17) =25.4 yards. 

Total, 53.0 yards. 

This is the number of yards the shell would miss the target 
laterally if the gun were fired with the deflection scale set at 50. 

From the range tables (column 18) we find that 3.17 yards at the 
target at 5000 yards range is corrected by one division on the 
deflection scale. Dividing by 3.17 the total number of yards to 
be compensated, we get the total number of divisions to the right 
of the fifty line that the deflection scale must be set in order to 
make a hit. This is 16.4. which, added to 50, gives the setting, 
66.4. . 

The initial azimuth setting should be as close an approxima¬ 
tion as it is possible to make, considering all the elements affect¬ 
ing it, in order that the lateral deviation of the fall of the shell may 
be as small as possible. The smaller this error, the easier it is for 
the spotter to bring the next shot on the target. 

516 . Range errors.—Even when we have standard conditions 
in ammunition and the atmosphere, it will be evident, from the 




Naval Gun Sights 


40 


preceding article, that when either the ship or the target is steam¬ 
ing there will be a range error in the fall of the shot. Under the 
usual conditions of battle, where the differences in course and 
speed of ship and target are not large, this error will probably be 
less than the danger space. A wind component in the plane of 
fire will decrease or increase the range according as it is towards 
or away from the ship. This error is comparatively small; for 
instance, with the 12-inch gun, when the target is distant 9000 
yards, a wind component of 12 knots in the plane of fire will cause 
a change of 21 yards in the range. (See column 13, Range I able, 
1912.) 

Range errors due to variations from standard conditions 
are as follows: 

(a) Change of range caused by variation of the density of the 
atmosphere .—A density above unity, the density for which the 
range strip is calculated (barometer 29.53 inches, thermometer 
59 0 F.), will make the shot go short; density below unity will 
make the shot go over ; other conditions being normal. For 
instance, a variation of 5 per cent will make a change in range of 
87 yards at 9000 yards range with the 12-inch gun. (See column 
12, Range Table, 1912.) This is an error that can be foretold 
by observation of the barometer and thermometer (outside) imme¬ 
diately before firing; if the change of distance of the target is not 
to be considerable, it can be satisfactorily compensated by applying 
a correction to the initial sight-bar range equal to the error picked 
out for the mean distance of the target. But as the error for a 
given density of the atmosphere varies with the range, it is evident 
that this method of compensation fails when there is a wide 
change in the distance of the target during the firing. 

(b) Variation in the range caused by variation in the tempera¬ 
ture of the pozvdcr .—Temperature of the charge above 90° F.. 
the standard for which the range strip is calculated, will make the 
shot go over : and temperature below 90 will make it short. 1 his 
is an error that can be avoided by keeping the magazines at the 
standard temperature by means of refrigeration or heating. On 
ships where these appliances are not installed, the worst feature of 
the temperature error is that magazines in different parts of the 
ship, for guns of the same caliber, will have different temperatures, 
and so the guns they supply will have different range errors, l or 



414 


Naval Ordnance 


instance, if the forward 12-inch magazine has a temperature of 
93 0 and the after 12-inch magazine has a temperature of 87°, 
when the target is distant 9000 yards, the forward 12-inch guns 
will shoot 53 yards over, while the after 12-inch guns shoot 
53 yards short. (See column 10 and explanatory note in Range 
Table, 1912.) Here is a difference amounting to more than half 
the danger space of 20-foot target-screen (84 yards at that range) ; 
consequently one turret may be hitting at the base of the target 
while the other is firing over the top edge. We must therefore 
apply corrections to the initial range to each gun in accordance 
with the temperature of the magazine that supplies it; and, since 
the temperature error varies with the distance of the target, we 
must select the correction for the mean range expected. If there 
is not much variation in the distance from this mean, this method 
of compensation will be satisfactory. 

(c) Change of range caused by variation in weight and coeffi¬ 
cient of form of the projectile. —A projectile of different weight 
from that for which the range strip is calculated will fall short if 
over weight, or will fall over if under weight. For instance, a 
12-inch projectile 5 pounds under weight will fall 20 yards over 
when the target is distant 9000 yards. (See column 11, Range 
Table, 1912.) Where the projectile is of standard weight, but is 
of a coefficient of form different from that for which the range 
strip is calculated, the trajectory will differ in range and drift. 
The new long-pointed projectile has a flatter trajectory than a 
blunt-pointed projectile of equal weight. Of late the inspection 
of projectiles before issue to the ship has become so reliable that 
errors in the weight need not be expected. When projectiles of 
different coefficients of form are supplied, range and deflection 
strips for each kind are furnished. 

517 . Arbitrary deflection scales.—The method of marking the 
deflection scales of sights in knots as described above is no'longer 
used, but an understanding of this method is necessary before the 
method of “ arbitrary ’’ divisions, which is the modern practice, can 
be understood. 

The method of controlling deflection by means of “ deflection 
boards ” and “ arbitrary scales ” was devised for the purpose of 
relieving the sight setters of the responsibility of keeping the 
deflection pointer on a designated deflection curve. The principle 


Naval Gun Sights 


4 i 5 


upon which the method is based is in no way different from the 
standard method of controlling deflection by means of knot curves. 
It differs in the method of application, in that one curve sheet 
upon which the knot curves are drawn performs the functions of 
the curve drums formerly fitted upon each individual sight. Many 
of the sights still in service are adapted for the use of either 
method of deflection control, and it will be seen by trying both 
methods that they give the same results, regardless of which one 
is used. 

The method of bringing the point of impact on the target in 
deflection in no way differs from that of bringing the point of 
impact on the target in range, except that deflection correction 
controls the angle of the sight with respect to the axis of the 
gun in the horizontal plane, while range correction controls it in 
the vertical plane. If the point of impact be short of the target, or, 
in other words, too low, the sight is raised; if the point of impact 
is to the left in deflection, the rear end of the telescopic sight is 
moved to the right, and vice versa. In either case it is the angle 
between the axis of the telescope and the axis of the gun that is 
changed, for range in the vertical plane, and for deflection in the 
horizontal plane. 

To arrive at a clear understanding of the principle of deflection, 
it should be comprehended that all deflection measurements can be 
reduced to angular measurements. If the horizontal angle between 
the axis of the gun and the line of sight be the same for all the 
guns of the same caliber firing, then the corresponding deflection, 
whether measured in knots or in yards, will also be the same for 
all those guns. It is thus seen that the sights for all types can be 
so constructed that the unit of measurement for deflection is an 
angle. 

Principle of Arbitrary Scales. 

518 . In the method of controlling deflection by the use of “ de¬ 
flection boards ” and “ arbitrary scales,” the unit of measurement, 
that is, the angle corresponding to one division of the scale, is the 
angle that is subtended by one-half of a chord of 0.2 of an inch at 
100-inch radius; that is, it is the angle whose tangent is .001. By 
using this unit of measurement, the divisions on the arbitrary scale 
( G, Plate II), are all equal to 0.1 an inch on all deflection boards 
for all sights for all guns, and all deflection boards are therefore 


4 i6 


Naval Ordxa n ce 


uniform in construction. The arbitrary scale fitted to each sight 
is graduated so that one division of the sight scale corresponds to 
this standard angle, whatever the value of the sight radius, and the 
actual magnitude of each such division in fractions of an inch 
therefore depends upon the value of the sight radius, and is deter¬ 
mined from it by proportion, as follows : 

x o . i , l 

~r- = -— , whence x— - 

/ IOO IOOO 

where x (in fractions of an inch) is the magnitude of the arbitrary 
division, and / is the sight radius in inches. These arbitrary scales, 
when once graduated, become permanent, regardless of any change 
in initial velocity or other modifications affecting the trajectory. 
The necessary corrections to provide for a qhange in initial velocity, 
for instance, would be made on the curve sheet (/, Plate II), and 
expensive and troublesome modifications in the manufactured 
scales on the sights would therefore be unnecessary. As the above- 
mentioned curve sheets are made on drawing paper, quickly and at 
small cost, it will be seen that changes in the ballistics of the guns 
could be made without great expense or delay in the supply of the 
necessary means for deflection control. 

In the triangle under consideration, the “ side opposite ” to the 
angle adopted as the standard angular unit of deflection, that is. 
the angle whose tangent is .001, is sometimes known as a “ mill,” 
because the side opposite is always one one-thousandth part of the 
side adjacent. In this case it is therefore the angle that corre¬ 
sponds to a deflection of 1 yard at 1000 yards range, and to a 
deflection of 10 yards at 10,000 yards range, etc. 

General Description of the Sight Deflection Board. 

519 . The “sight deflection board,” as shown on Plate II, as 
furnished to ships, is simply a means of mechanically turning a 
determined deflection in knots into the units of the arbitrary scale, 
and at the same time applying the drift correction for the given 
range. It consists of a wood or aluminum board. A, about 20 
inches square. On each side is a rack, B , which is secured by wing 
nuts, C. Across the top, and also held by the wing nuts C, is a 
metal strip, D, which carries the sliding pointer, E. The scale of 
arbitrary divisions, G, slides up and down the board parallel to 




Naval Gun Sights 


41/ 


itself upon the racks, B, as guides. A pinion on each end of the 
shaft, F, runs upon the racks, B, and prevents canting of the 
scale, G. The sliding pointer, H, is carried upon the scale, G, for 
use in keeping track of the divisions of the scale used. The curve 
sheet, J, is cut to fit under the racks, B, where it is held from 
slipping, after being properly adjusted, by the wing nuts, C. In 
placing the sheet on the board, it must be so adjusted that the 
reference line, XX, will always be under the 5° mark of the 
scale G as the latter is run up and down from top to bottom of the 
board. (It will be noted on the plate that the line XX, which 
should intersect the 50 curve at zero yards range, is slightly to the 
right of that curve at the 1000-yard range mark at the top of the 
curve sheet, which is of course as it should be. 1 he slight diver¬ 
gence of the 50 mark of the scale G from the line A A that is notice¬ 
able on the plate is undoubtedly due to parallax in taking the photo¬ 
graph, the camera apparently not having been set up directly in 
front of that point.) 

The legend on the curve sheet shows for what sights, for what 
caliber of gun. and for what initial velocity it is to be used; and 
also indicates, for the information of the spotters and sight setters, 
the value in knots at some given range to which the divisions on the 
arbitrary scale correspond. 

Method of Use. 

520 . The deflection board is designed primarily for use in the 
plotting room, but it can be used at any other point that may be 
desired, such as the spotter’s top or in the tui rets. 

When about to open fire, the knot curve to be used should be 
determined by computation (or by the use of the gun eiiot com¬ 
puter) in the same manner as has been explained for the deflection 
sight scale marked in knots; but this would no longer be sent out 
to the guns as the setting of the sights in deflection. Instead, the 
pointer E is placed at the top to indicate the curve to be used (the 
45-knot curve on Plate III). The scale G is then run down the 
board to correspond to the range to be used (14,000 yards on the 
plate). The pointer H is then run along the scale G until it is 
over the proper curve on the sheet (45 knots), and the leading 
under the same pointer on the scale G will then be the number of 
divisions of the arbitrary sight scale at which the sights should 


28 


4 i8 


Naval Ordnance 


be set to give the desired deflection (40 divisions on the plate). As 
the curves on the sheet are the drift curves for the gun, the sight 
setting in arbitrary divisions of the scale thus found will of course 
include the drift correction. 

As the range varies during the firing, the scale G is moved up 
and down to follow it, and the pointer H is moved to the right or 
left to keep it over the proper curve on the sheet (45 on the plate). 
The pointer H will then always indicate on the scale G the proper 
sight setting in deflection in the markings of the arbitrary scale. 

In case the spotter's corrections indicate the use of a new curve 
at any time, the pointer E is shifted to that curve, and the new 
readings for the arbitrary scale are read off from the scale G by 
the pointer H (which is now following the new curve) and sent to 
the sight setters. 

By this process the sight setters are relieved of all responsibility 
in regard to the deflection setting other than that of setting the 
sight for the scale readings which they receive from time to time 
from the deflection operator, and it is no longer necessary for them 
to be continually following a drift curve on the sight drum as 
the range increases or decreases. 

521 . The method of control described above involving the use 
of the board gives greater accuracy than the one using curve 
drums on the sights, as the deflection board permits the curve 
sheets to be made on a larger scale. It is not necessary, however, 
to continue the use of the deflection board after the initial data has 
been obtained for opening fire. The board may be used to deter¬ 
mine the setting of the sights in deflection by the arbitrary scale 
for firing the first shot ; and after that the spotter can indicate the 
deflection changes in terms of the arbitrary scale, providing he 
knows approximately the value of the arbitrary divisions in knots 
or yards at the target, for the approximate range at which the 
firing is being conducted (in yards, this is one one-thousandth of 
the range in yards, as already seen) ; and, after shots are seen to 
be hitting at the proper point, they can then be held at that point 
by giving the spotter’s corrections in terms of the arbitrary scale, 
as soon as the point of impact appears to creep to the right or to 
the left, and before it can creep off the target. 

522 . Multiplying scales.—With high-power guns it is often 
impracticable to design the pivot bar long enough for distinct 



CHAPTER XII. PLATE II. 

B C 



DEFLECTION BOARD. 

























































































































































































Naval Gun Sights 


419 

spacing and numbering of the range divisions at 100-yard intervals 
and the deflection divisions at 2-knot intervals. In such cases the 
range scale is placed on a dial geared up from a rack on the sight 
bar, and the deflection scale is placed on a drum geared up from a 
rack on the rear end of the pivot bar; this amounts to a mechanical 
magnification of the scales. As the details of the various methods 
of accomplishing it are readily understood upon examining the 
sight mount, no illustrations are given. 

In sights of this type great care must be taken to keep lost motion 
out of the multiplying gears; this would result in sight setting 
errors in range or in deflection, or in both. Such errors are 
detected as follows: Lay the gun by the bore sight on some fixed 
mark; then move the rear end of the sight bar up and to the right 
until the line of sight is directed to some other point whose posi¬ 
tion with reference to the first mark is fixed; note the exact read¬ 
ing of range and deflection scales. Now run the sight bar well 
up above, and move the pivot bar well to the right of these read¬ 
ings ; then by motion down and to the left come back to the noted 
readings. See that the axis of bore is directed to its mark; then, 
if the line of sight is not directed to its mark there is lost motion 
between the pivot bar and the scales. The errors may be due to 
any of the following causes: 

(a) Lost motion in the multiplying gear. 

(b) Bending of the sight bar, due to very tight fitting of sight 
axes. 

(c) Play in the front end of the sight bar, due to loose fitting 
of the sight axes. 

The above test, in the case of parallel-motion sight mounts, 
should be made in dry dock or in still water with the ship moored 
to the dock unless both marks can be set up on the ship; the reason 
for this will appear later when that type of turret sight mount is 
described. 

523 . The calibration of a gun is determined by firing a string 
of accurately aimed shots at a target bearing nearly abeam, whose 
distance, at a mean battle range, is accurately measured. The 
point of fall of each shot is plotted as accurately as possible. The 
setting of the sight is the same for each shot, making the sight- 
bar range the same as the actual range; and care is taken that 
there are no errors in the adjustment or in the mechanism of the 


420 


Naval Ordnance 


sight mount, or in the adjustment of the telescope. Prior to this 
the graduations of sight strips should be checked up. The ship 
is moored in still water and normally trimmed; the powder is all 
of one index and is kept at the same temperature for each shot 
of the string—preferably as near as possible to 90°; the projec¬ 
tiles are brought to standard weight if any variation is found; 
and the density of the atmosphere is carefully recorded through¬ 
out the string. The mean force and direction of the wind on the 
range are determined as well as possible, but on account of the 
difficulty in getting reliable data of this kind, the firing should be 
done in nearly calm weather. 

After applying to the mean point of impact the corrections for 
height of bull’s-eye from the water, variation from standard 
density of atmosphere, variation from standard temperature of 
powder, and tfie effect of a wind component in the plane of fire, 
and across the plane of fire, there will still be found a discrepancy 
between the setting of the sight in range and azimuth and the mean 
point of impact. A small part of the discrepancy may be due to 
unlevel installation of the gun mount or improper adjustment of 
the frictionless trunnions, either of which will produce “ tilting ’’ 
of the line of sight and consequent vertical and lateral errors. 
These two errors can now be compensated by shifting the range 
and azimuth strips; for example, we find that the mean point of 
impact for a string of four shots at a target distant 7500 yards is 
250 yards over and 25 yards right, the sight being set to range 
7500, deflection 50. Correcting the observed mean error for the 
height of bull’s-eye and the variations from standard conditions, 
we find the standard error is 100 yards over and 12 yards right. 
To calibrate this gun in range we would lower the sight bar to 
reading 7400, then shift the range strip to make it read 7500. To 
calibrate the gun in azimuth we would set to the fifty-line (when 
range reads 7500), then shift the azimuth scale to the left the 
number of knots corresponding to 12 yards lateral error at 7500 
yards range. (For instance, with 12-inch guns, column 18 of 
Range Table, 1912, gives 60 yards deviation for 12 knots; then 
1 knot corresponds to 5 yards and 2.4 knots correspond approxi¬ 
mately to 12 yards.) 

Calibration errors of different guns of one caliber will usually 
be found different; when each has had its correction applied, all 


Naval Gun Sights 


421 


guns of this caliber will bunch their shots well, when the target 
is at a distance that does not differ greatly from the distance of 
the calibration target and when its bearing is about the same, 
relative to the ship, as the bearing of the calibration target. A 
change of index of powder from that with which the calibration 
tests were made will make but little difference in the results, pro¬ 
vided the powder is in good condition. 

When calibrating a ship’s battery, one gun is selected as the 
standard gun. This selection is made because its standard error 
is small and because the four shots from the gun have given the 
most consistent results. The errors of the other guns are com¬ 
pared with the standard gun, and the sights are changed to bring 
all the guns to the standard gun, after which all the guns will 
bunch their shots—which is what we strive for in naval gunnery. 

Types of Sights and Sight Mounts. 

524. The line of sight was defined in paragraph (4), Art. 506, 
as the straight line prolonged through the front and rear sight 
points. There are three principal arrangements for establishing 
these sight points, any one of which may be applied to the sight 
mounts described in this chapter. These arrangements are named : 
(1) The open sight, (2) the peep sight, and (3) the telescope sight. 

525. The open sight is the earliest and least efficient arrange¬ 
ment of the sight points. As shown in Fig. 86, the front sight point 
is the apex of a cone and the rear sight point is the bottom point 
of a V-shaped notch. (Also see Plate I.) 

The chief defect in the open sight lies in the fact that the eye 
cannot simultaneously see the target and the two sight points 
distinctly; it must accommodate (focus) successively for three 
different distances. This sight is not only fatiguing to the eye but 
is inaccurate even under the most favorable conditions (namely, 
when both gun and target are still, and there is no difficulty in 
keeping the optical axis coincident with the line joining the sight 
points) ; this is because changes in the direction and intensity of 
the illumination of the front sight point will make an apparent 
change in its position and a consequent apparent change in the 
direction of the line of sight. In addition to the above, there is 
no magnification of the target, and a considerable portion of its 
area is obscured by the sight points. I his type of sight is rapidly 


422 


Naval Ordnance 


disappearing from the service, and its use probably will soon be 
restricted to revolvers and automatic pistols. 

In Fig. 86 it will be seen that there is no pivot bar. The sight 
bar is straight, instead of being machined to an arc of a circle. 
The compensation for drift is accomplished (approximately) by 
fitting the sight-bar bracket so that the sight bar is inclined slightly 





to the left at a permanent angle. This is illustrated in Figs. 87 and 
88. - In Fig. 87, with the sight bar at zero, the front sight, rear 
sight and bull’s-eye are in line ; in Fig. 88, with the sight bar raised 
and the gun elevated until the two sight points and bull’s-eye are in 
one plane,-it will be seen that the line of sight is pointing to the 
right of the bull’s-eye. Now, to bring it on, we must train the 



























Xaval Gun Sights 


423 


gun a little to the left, which in a measure will compensate the 
right-hand curvature of the trajectory. 

In sights that are inclined to the left at a permanent angle to 
compensate for drift, the drift is over-compensated at short ranges 
and under-compensated at long ranges. In the installation of 
sights of this character it is assumed that the drift is proportional 
to the range, which, however, is not the case, as the rate of in¬ 
crease of the drift increases with the range. 



fte-er/L/r/ff 

Civ rise 


/?£ sivmee/ 
Ctsrre. 

Fig. 89. 


526 . The peep sight is an improvement on the open sight, for 
the reason that it requires the eye to focus successively for two 
distances instead of for three. Fig. 90 shows the essential parts 
of this type of sight. 





1 - 

-**—-; - * / 

°f y._ 


T- 

Y C t w f ro *■ <. a 

'' S1 de 


Fig. 90. 


The front sight point in a peep sight is about the same as in an 
open sight; but instead of a notch for the rear sight point there is 
a circular hole in a diaphragm (d. Fig. 90). 1 he line of sight 

is defined by the tip of the front sight point and the center of the 
peep hole. It is evident that the accuracy of this type of sight 
depends primarily on the accuracy with which the eye is centered 
at the peep hole; if r be the radius of the hole and R be the dis¬ 
tance between it and the front sight point, by moving the axis of 
the eye from the center of the hole over to the edge we shall make 







424 


Xaval Ordnance 


an angular error, called parallax, in the line of sight that is equal 


to tan -1 J —. 
R 


Now the value of r determines the sectional area of 


the pencils of light from the target that reach the eye. Since the 
apparent brightness of an object of a given intensity of illumina¬ 
tion per unit of area is dependent on the sectional area of the 
pencils of light from it that enter the eye, it is evident that if r u 
the radius of the eye pupil, be larger than the radius of the peep 
hole, the apparent brightness of the target as seen through the 
peep hole is to its apparent brightness when viewed by the unob¬ 
structed eye as the ratio Since the radius of the normal eye 

. r ' . 

pupil when dilated at night is one-tenth inch, if our peep sight is 
to be effective at night the radius of the peep hole should be at 
least one-tenth inch ; but with this value of r, it is impracticable 
to make R, the distance to the front sight, great enough to ensure 
sufficient accuracy. For this reason, even if there were no others, 
the peep sight could not be made an efficient night sight. How¬ 
ever, in the daytime the apparent brightness of the target is of no 
consequence, and we can make the peep hole small enough to 
reduce the parallax error to a negligible quantity. 

The peep sight is installed on many of our sight mounts, and 
was designed to be the night sight, being arranged so that the 
front sight point can be illuminated; but in August, 1905, after 
some experiments in the subject of night sights at the Naval Gun 
Factory, the telescope was developed to such an extent that its 
gain in efficiency over the peep sight for night work is something 
over 3000 per cent. The peep sight is therefore retained merely 
as a stand-by in event of injury to the telescope. 

527 . The telescope sight is the most convenient and most 
efficient means of establishing the sight points. It may be defined 
as the combination of two systems of lenses on a common axis 
spaced so that the second focal plane of the first system (the 
objective equivalent) is coincident with the first focal plane of the 
second system (the eye piece equivalent), which plane contains a 
pair of intersecting cross wires or etched cross lines. 

There are three points in the telescope that determine the line 
of sight; namely, the intersection of the cross lines, and the first 
and second unit points of the objective equivalent. The stability 


Naval Gun Si<;iits 


4-5 

of the line of sight with reference to the sight mount therefore 
depends on the rigidity of the point of intersection of the cross 
lines and all optical parts in front of it. 

The telescope is so attached to the gun that the line of sight 
can be set at any desired angle with the axis of the gun. Some 
confusion exists as to the nomenclature of “ telescopic sights.” In 
the case of telescopic sights the word “ sight refers to the heavy 
steel yoke attached to the gun slide or to the trunnion, while the 
word “ telescope ” refers to the optical instrument through which 
the gun pointer sees the target. 

Telescope Sights. 

528 . There are four varieties of telescopes used as gun sights 
in the navy. 

The first type has the universal focus; 1. c., has no adjustment 
whatever, for focusing. 1 he first of these was of 2 \ power, and 
had no means for focusing the eye piece to suit individual eyes. 
This form is obsolete, as modern fixed-power telescopes have a 
means of focusing the eye piece so as to accommodate the indi¬ 
vidual eye. 

The second type is the standard variable-power telescope. The 
variable power is secured by moving the eye-piece tube in and out 
and then clamping it at the desired power, after which the tele¬ 
scope is focused. 

In the modern type of variable-power telescope used for turret 
trainers, two magnifications are obtained by moving the position 
of the erecting system. Distinct vision is obtained only at two 
powers in this type. 

Another form of variable power is obtained in the continuously 
variable-power telescope. By means of a spiral on the inside of the 
telescope, the position of the erecting system is changed, and at 
the same time the relative positions of the lens of the erecting 
system themselves are changed. I his gives a clear, distinct vision 
while changing from one power to another. 

The third type is the prismatic telescope , which has two 90° 
elbows, so that an indirect line of sight is obtained. This telescope 
is fitted with prisms, to obtain the required change of direction. 

This type was originally intended for turrets only, but is now 
supplied for broadside guns. 


Naval Ordnance 


426 

The fourth type is the checking telescope, which may be any of 
the above three types fitted with a second eye piece, so that two 
observers may see through the telescope at the same time. This is 
attained by means of a prism inserted in the path of the rays from 
the objective to the primary eye piece. One disadvantage of this 
scheme is that each observer gets only half the light that he would 
receive ordinarily. 

As this checking eye piece is intended for use in training 
pointers, the latest telescopes are fitted so that the checking eye¬ 
piece system can be thrown out at will. 

529 . Advantages of the telescope sight.—The first point of 
superiority of the telescope as a sight is the fact that the eye is 
focused for any one distance, instead of successively accommodat¬ 
ing for three, as with the open sight, or successively for two, as 
with the peep sight. This is because the eye, when the adjustment 
of the telescope is correct and the target is at long range, sees, 
through the eye-piece equivalent, the intersection of the lines and 
the image of the target in one plane. Furthermore, under the 
above conditions the pencils of light that emerge from the eye 
piece are parallel pencils, and the accommodation muscles of the 
normal eye are at rest when it is receiving such pencils. With the 
open sight and pee]) sight, if the eye is moved ofif the line of sight, 
errors in pointing will occur; but with the telescope, motion of the 
eye either across or along the line of sight will not afifect the 
accuracy of pointing, provided the telescope is properly adjusted 
and the target is at long range. For as long as the eye is in some 
position where it will receive a part of some pencil that emerges 
from the eye piece after diverging from the intersection of the 
lines, it will see the intersection of the lines and some part of the 
field of view. There are limits along the axis of the eve piece and 
across it within which the eye should be placed if it is desired to 
utilize the full field of view and receive the maximum amount of 
light from the target; however, the rubber buffer fitted on the eye 
end of the telescope makes it easy for the eye to place itself within 
the proper limits. 

1 he next point of superiority of the telescope is its magnifying 
power. At modern battle ranges it is necessary to have an apparent 
enlargement of the target in order to point the gun with sufficient 
accuracy. Where F is the focal length of the objective equivalent, 


Naval Gun Sights 


427 

and / is the focal length of the eye piece equivalent, the magnify- 

F 

ing power of the instrument will be M = - j- diameters. For 

instance, if F be 20 inches and / be 2\ inches, the magnifying 
power will be 8 diameters. When using this telescope on a target 
distant 8000 yards, we can lay the gun with as much facility as 
we could lay it on the same target distant 1000 yards with a sight 
that has no magnifying power. But the increase of magnifying 
power is attended with a corresponding decrease in the field of 
view. Roughly, the field of view of any telescope will be 35 0 
divided by the magnifying power. We are therefore restricted in 
the application of this point of advantage by the size of field of 
view which is large enough to permit the gun pointer to “ pick up 
the target. 

Another point of advantage in the telescope sight is the fact that 
the size of the emergent pencils does not affect the accuracy as 
does enlargement of the hole in the peep sight. W hen M is the 
magnifying power and A is the aperture of the telescope, the diam¬ 
eter of emergent pencils will be • By making the proper relation 

between A and M we can utilize the full area of the dilated eye 
pupil at night; and so, instead of making it more difficult to pick 
up a target when looking through the sight than it is when looking 
with the naked eye, we can, with the new telescopes in service, 
pick up and lay on a target that is so dimly illuminated as to be 
invisible to the naked eye. But the proper relation between 
aperture and magnifying power is only one of several points in the 
design of our telescopes (some of which are confidential) that 
make them highly efficient night sights. 

530 . Parallax .—When the image of the target and the cross 
lines in the telescope do not lie in the same focal plane in the 
instrument an error exists known as Parallax. 

It is easily detected by laying the telescope on a fixed mark, 
keeping it in a fixed position, and then moving the eye up and 
down or sideways across the eye piece. If there is no apparent 
motion of the intersection relative to the image, they are both in 
the same plane; if the intersection appears to move over the image 
in an opposite direction to the motion of the eye, the image lies 
forward of the lines; if it appears to move over the image in the 
same direction as the motion of the eye, the image lies in rear of 


428 


Naval Ordnance 


the lines. The second-mentioned condition would be due to incor¬ 
rect adjustment of the telescope; the third condition would be due 
to incorrect adjustment of the telescope; the third condition would 
be due to incorrect adjustment if the mark selected for the test is 
more than a mile distant. When a telescope has an objective 
equivalent of a moderate focal length like that in our telescope 
sights, and the telescope is in correct adjustment, the image of an 
object distant anywhere from infinity to a mile is not perceptibly 
in rear of the second focal plane of the objective equivalent—the 



position of the cross lines. Actually, however, the image is in 

772 

rear of this position a distance Y = ~where F is the focal length 

of the objective equivalent, and X is the distance of the object 
measured forward of the first principal focus ot the objective 
equivalent. From this it is evident that, if our telescope is 
adjusted for long range, the image of a miniature target as close 
as the end of a Morris 1 ube boom (or in the corresponding posi¬ 
tion in a dotter), will be so far in rear of the cross lines that it will 
give a very large amount of parallax. 

Formerly, to obviate this condition the telescope was re-focused 
(by increasing the distance between the cross lines and objective 
equivalent) to make the image of miniature target and cross lines 
coincident; but this is bad practice, for the reason that it involves a 
disturbance of the bore-sighting adjustment, which makes it neces¬ 
sary for the ship to go into still water, readjust the telescope for 





















































Naval Gun Sights 


429 

long range, and bore sight again before the gun can be fired. We 
now have an optical instrument called a focusing cap which makes 
it possible to use the telescope on a near miniature target without 
disturbing its adjustment or the adjustment of the sight mount 
for long-range firing. Focusing caps consist of a positive lens 
(7) and a negative lens (8) so mounted that the distance between 
the two lenses may be varied at will. The two lenses are held at 
the desired distance apart by the clamping ring (6). By means of 
the three adjusting strips (4) and the adjusting screws (5) the 
focusing cap can be adjusted to most telescopes. Special base 
fittings are required with the latest marks of telescope, but in 
such cases the special bases are furnished with the caps, (big- 9 1 •) 
In using, the telescope itself should be focused on a distant 
object until free from parallax. 1 he focusing cap is then shipped 
in place on the objective end of the telescope, the telescope is 
directed toward the dotter target, and the draw tube (2) is moved 
in and out until the image of the target is clear and distinct and 
the cross lines are sharp and without parallax. 



531 . Parallel-motion sight mounts.—When the opening for 
the line of sight is in a hood on the roof of a turret, it is im¬ 
practicable to attach the sight mount directly to the slide; the 
pivot bar is so far from the trunnions that elevation of the gun 
causes it to move to the rear and downward a considerable dis¬ 
tance. This condition is illustrated by Figs. 92 and 93, which 
show, respectively, the relative position of gun and line of sight 
when the gun is level and when it is elevated. In Fig. 93 it wl11 
be seen that the line of sight is below the opening in the hood, 
although the gun is not at extreme elevation. 















430 


Naval Ordnance 


532 . Roof sight mounts are therefore indirectly attached to the 
slide by a parallel-motion mechanism; the pivot bar with the 
fittings for its horizontal and vertical axes, the sight bar, and sight- 
bar bracket are mounted on an arm, called the connecting arm , 
that has a horizontal axis at its upper end in a fixed position with 







- 

1 ; 



• 


Fie. 94. 


reference to the deck lug, and is connected to the slide so that it 
will move in elevation with an angular motion exactly equal to 
the angular motion of the gun in elevation. One method of im¬ 
parting this motion to the connecting arm is shown in Fig. 94. 

In big. 94 the connecting arm pP has its fixed axis at P in the 
sight bracket B, which is made up of two parts bolted to the deck 





























Naval Gun Sights 


43 i 

lug. At its rear end it engages the bar pt, called the connecting 
bar, on the shaft bolt p; this in turn is connected to the slide on the 
shaft bolt t. In the parallelogram PpTt, the side PT = side pt, and 
side pP — side Tt; P and T are fixed points of the parallel motion, 
T being the axis of trunnions of the gun. A guide block b, which 
is a part of the connecting arm, works in the circular slot L, in the 
guide bracket, machined to arcs of circles centered in the axis P. 
The guide bracket is bolted to the lower part of the sight bracket; 
with the guide block, it prevents lateral bending of the connecting 
arm. The connecting arm will work through angles exactly equal 
to angles described by the axis of the bore of the gun only when 
the following conditions are maintained : 

(a) That the axes P, p, and t are installed exactly parallel to 
the axis of the trunnions. 

(b) That the distance from the axis P to the axis p is exactly 
equal to the distance from the axis t to the axis of the trunnions 
T; also that the distance from the axis p to the axis t is exactly 
equal to the distance from the axis P to the axis of the trun¬ 
nions T. 

Although the parallel motion may have been installed in con¬ 
formity with the above conditions, it is evident that any bending or 
springing of the connecting arm or the connecting bar will dis¬ 
tort the parallelogram and cause pointing errors that may be either 
vertical or horizontal. A material looseness caused by wear in the 
working surfaces will result in vertical errors in pointing. Any 
change of the position of the trunnions with reference to the deck- 
lug will also distort the parallelogram. When the gun is being- 
elevated, the slide tends to shift forward in the deck lugs; so, 
if there is too much clearance in the trunnion seats, the axis of 
trunnions will shift forward far enough to make a material eiroi 
in the parallelogram. Upon depressing the gun, the shift is in the 
opposite direction. Naturally, any adjustment of the frictionless 
trunnions that is different from the adjustment at the time the 
parallel motion was installed will affect the parallelogram. 

533 . Another form of parallel motion is shown in big. 95. 
The connecting bar pt and shaft bolt t of Fig. 94 are replaced by the 
circular cam C that is bolted to the slide; the center of curvature 
of this cam is at a point t which is in a fixed position with lcfeience 
to the slide and axis of trunnions, such that 11 —pi and tp— TP. 


432 


Naval Ordnance 



Fig. 95 - 



Fig. 96. 


H y Tll 





































Naval Gun Sights 


433 


The rear end of the connecting arm contains a shaft bolt p set up 
in the cam block b. The flat face of the cam must be installed 
exactly in a plane perpendicular to the axis of trunnions. The 
parallelogram then is PpTt, as in the preceding figure. 

The advantages of this form of parallel motion are: No matter 
how long the connecting arm may be, the cam prevents its rear 
end from being sprung laterally; and, as there are fewer working 
parts, there are fewer errors due to wear in bearing surfaces. 

534 . A method of mounting the pivot bar, sight bar and sight 
bar bracket on the connecting arm is shown in Fig. 96. It will be 
seen that the horizontal sight axis PP' is coincident with the upper 
axis of the connecting arm. It is formed by the two trunnion bolts 
P and P' tapped into the jaws of the bracket; these are the bear¬ 
ings for the jaws of the connecting arm and for D, the pivot-bar 
block , into which is tapped the bolt A that forms the vertical sight 
axis AA'. The sight-bar bracket is bolted to the connecting arm 
at its rear end. 

535 . Tests of parallel-motion mechanism.—For tests of 
parallel motion mechanism, two observers are required—one to 
look along the axis of bore, the other to look along the line of sight. 

First inspect for lost motion as follows: Direct the axis of bore 
to a distant mark by motion of the gun, and direct the line of sight 
to the same mark by motion of the pivot bar. Move the gun to 
extreme elevation, and then depress it until the observer at the 
breech notes the axis of bore on the distant mark. 1 hen move the 
gun to extreme depression and elevate until the observer at the 
breech notes the axis of bore again on the mark. Each time the 
observer at the breech is exactly on, the observer at the sight 
should also be exactly on. Lost motion may appear as follows: 
Both may be on when the axis of bore has been elevated to the 
mark, but the line of sight will point high after the gun has been 
depressed to the mark; or else both may be on when the axis 
of bore has been depressed to the mark, but the line of sight will 
point low after the gun has been elevated to the mark. The error 
may be due to any of the following conditions: 

(a) Looseness in the bearings of the parallel motion. 

(b) Bending of either the connecting arm or connecting bar, 
caused by very tight bearings. 

(c) Shifting backward and forward of the axis of trunnions, 
caused by too great clearance in the trunnion seats. 


-9 


434 


Naval Ordnance 


After the parallel motion has passed a thorough test for lost 
motion, it should be tested for accuracy of the parallelogram as 
follows: Elevate the gun until the axis of bore is directed to the 
center of a heavenly body in the west, selecting a time that will 
give extreme elevation to the gun. Simultaneously, by motion of 
the pivot bar, bring the line of sight to the center of the same 
body. When the body is near the horizon, lay the axis of bore on 
its center; now, if the line of sight is also on, we can be satisfied 
that the parallelogram is properly proportioned and that the upper 
axis of the connecting arm is parallel to the axis of the trunnions. 



brte/Cet 


TfJesCof’ e 
L/J(r 



pH! ] 









/ -J -Hi 



['if; 

: 



A 

r M 


If the parallelogram is not properly proportioned, the line of sight 
will be high or low when the axis of bore is on ; if the upper axis 
of the connecting arm is not parallel to the axis of the trunnions, 
the line of sight will point to the right or left when the axis of 
bore is on. It is obvious that, before making this test, we should 
see that the frictionless trunnions are correctly adjusted to the 
positions they are to he in during firing. 

536 . Turret trainer’s sight mount.—The trainer’s sight mount 
in turrets is usually placed between the two guns. It is not con¬ 
nected to either gun slide but has two parts that are in a fixed posi- 
























Naval Gun Sights 


435 


tion relative to the two pairs of deck lugs. In Fig. 97 these fixed 
parts are the sight bracket and the azimuth head. 

The pivot bar is capable of motion in azimuth about the vertical 
sight axis vv'. This axis must be installed exactly perpendicular 
to the plane of the roller path of the turret. The rear end of the 
pivot bar travels in the circular slot in the azimuth head and 
carries the pointer P for indicating the setting in azimuth. It will 
be seen that the pivot bar has no vertical motion; therefore, in 
order that the trainer may keep the target within the field of view 
of his telescope while the ship is rolling, the telescope holder has a 



trunnion mounting on the pivot bar. 1 he axis of this trunnion 
mounting, tt', must be installed exactly at right angles with the 
vertical axis vv'. The azimuth scale is engraved on the deflection 
arum D, of which a development is shown in Fig. 98; the gradu¬ 
ations on this drum are determined from the graduations on the 
azimuth plate on the pointer's sight. In order that the azimuth 
changes of the trainer's line of sight shall equal the azimuth 
changes of either pointer’s line of sight, the drum must be rotated 
by the handle h until the reading by the scale and small reference 
pointer p on the end is opposite the range reading set on the 
pointer’s sight; then, when the pivot bar is moved to the left or 
right until the reference mark on the pointer P touches the speed- 


























43^ 


Naval Ordnance 


line that has the same number as the speed line to which the 
pointer's sight is set, the azimuth change from the bore sighting 
position will be the same in each sight. 

537 . Adjustment of trainer’s sight.—Turret guns are required 
to be installed so that the axes of the bores are parallel or converge 
slightly. In bore sighting all, three sights, if the firing is to be 
at long range, the position of the trainer’s line of sight should be 
midway between the pointers’ lines of sight when all scales read 
zero; this, of course, puts both pointers a little bit off laterally 



when the trainer is on. At short-range firing, where this dis¬ 
crepancy will amount to a considerable portion of the area of the 
target, the trainer should lay his line of sight a certain amount to 
the right of the bull’s-eye when the left gun is to fire, or a certain 
amount to the left when the right gun is to fire, the amount he is 
to aim off the bull’s-eye being half the divergence between the two 
pointers’ lines of sight. 

538 . Yoke sight mounts.—The two lines of sight, one for the 
pointer and one for the trainer, with guns not mounted in turrets, 
are now carried on one sight mount which is a modification of the 


























Naval Gun Sights 


447 


type shown in Plate I. This modification, which is called the yoke 
mount ; is illustrated by Fig. 99. 

Instead of a pivot bar we have a yoke Y which amounts to a 
pivot bar spread out wide enough to carry a telescope on each 
side of the gun. The rear end of the yoke works in the azimuth 
head on the sight bar in the same manner as the rear end of the 



/ r # M f ro k t 


Fig. 100. 


pivot bar in Plate I. The horizontal sight axis is formed by a 
shaft hh', called the saddle pm, in a casting C called the saddle, 
and engaging a casting R called the rocker. I he vertical sight 
axis is formed by the pin vv' which centers the yoke in the rocker. 
The upper and lower side edges of the rocker, a, b, c, d, are 
machined to arcs of circles centered in vv' to a working fit in the 
yoke; this gives stiffness at the positions H and H' where the 



























438 


Naval Ordnance 


castings called telescope holders are connected to the yoke. The 
left-hand telescope holder carries the pointer’s telescope; in bore 
sighting, this line of sight is adjusted to the axis of bore by motion 
of the yoke in the azimuth head and by motion of the sight bar. 
The sight-hand telescope holder carries the trainer’s telescope, 
and is adjustable with reference to the yoke, so that this line of 
sight can be directed to the point of intersection of the axis of bore 
and the pointer’s line of sight; the mechanism of this adjustment 
is not shown in the figure. The sight bar, and sight-bar bracket, 
are the same in principle as those in Plate I. 

539 . Periscopic sights for broadside guns.—With the sight 
mount shown in Fig. 99, the wide distance between the two lines of 
sight makes the opening in the gun shield very large. Besides 
this, the effective arc of train of the gun is considerably less than 
the actual arc that the gun covers in moving from one edge of 
the port to the other; the pointer’s line of sight will be maskbd 
when the gun is at extreme train left, and the trainer’s line of 
sight will be masked when the gun is at extreme train right. 
These two faults are corrected by using prism telescopes in which 
the line of sight, in effect, is turned through two right angles, as 
shown in Fig. 100. The sight mount for these telescopes is prac¬ 
tically the same as the mount shown in Fig. 99, so it will be suffi¬ 
cient in Fig. 100 to show a portion of the yoke, with the telescope 
holders, and the positions of telescopes relatively to the gun when 
the sight bar is set at zero. (See also Chapter X, Plate II, Fig. 1.) 

540 . Periscopic sights for turret guns.—Troubles with the 
adjustment and difficulties with the installation of parallel-motion 
sight mounts have led to the design of a prism telescope in which 
the line of sight is, in effect, turned through two right angles. 
This telescope is placed so that it projects through a hole in the 
side of the turret in line with the axis of the trunnions of the gun, 
as shown in Fig. 100. It is carried in a sight mount similar in 
principle to the mount shown in Plate I; being attached directly 
to the slide and trunnion, it has no parallel-motion mechanism. 

The fixed parts of the sight mount are the sight-bar bracket B, 
bolted to the slide and trunnion, and the sight bracket S, bolted to 
the slide. The pivot block engages the shaft pin w ', which jour¬ 
nals in the sight-bar bracket, and forms the vertical sight axis. 
The pivot bar is machined to bearings on the top and bottom of 


Naval Gun Sights 


439 


the pivot block in order to give lateral stiffness to the support for 
the telescope holder; it also engages the pin lih' which is tapped 
into the rocker and forms the horizontal sight axis. The two 
sight axes intersect at right angles. The rear end of the pivot bar 
works laterally in a slot in the azimuth head, which, with the sight 
bar and sight : bar bracket, is practically the same as in Plate I. On 



Fig. ioi. 


account of the flatness of the trajectory of the gun with which this 
sight is used, the range and deflection scales are of the multiply¬ 
ing type. The directions of the line of sight at the objective end 
and eye-piece end of the telescope are shown in dot-and-dash lines 
on the plan. The outer end of the hole in the side wall of the 
turret is partly covered by a small hood called the blast hood. 





















































440 


Naval Ordnance 


541 . The trainer’s telescope in turrets fitted with periscopic 
sights is of the same design as the pointers’ telescopes, but is 
mounted vertically instead of horizontally. The opening for it, in 
the turret armor, is in the front face of the turret between the guns 



E l e r Cl t L o h' 



and close to the shelf plate. On account of the restricted space 
available, the mount for this sight, as shown in Fig. 102, is some¬ 
what different from the trainer’s sight mount shown in Fig. 97. 
Here, instead of a pivot bar, the part that carries the telescope 




























Naval Gun Sights 


44' 




trunnions moves in a slot in the azimuth head which is machined 
to the arc of a circle that has a virtual center corresponding to the 
vertical axis of the pivot bar in Fig'. 97. The deflection drum and 
pointers are practically the same as in Fig'. 97, but the sight-setter’s 
position is in front instead of in rear of the trainer. 

542 . Latest turret sights.—On the latest turret guns a yoke 
sight is installed, but instead of being pivoted to the top of the 
slide it is pivoted underneath. It is fitted with a prism telescope. 
The line of sight from the objective end of the telescope is under¬ 
neath the guns. The guns are fitted with shields which give the 
protection made necessary by the larger port openings in the front 
face plate of the turret. 



Fic. 103. 

543 . A bore sight is a telescope sight mounted as shown in 
Fig. 103. The telescope holder H screws into a threaded hole in 
the center of the casting D, called the breech disk, which is 
machined to fit into the screw box of the gun with which the bore- 
sight telescope is to be used. The telescope is mounted in its 
holder by a ball-and-socket joint J —the center of the ball, c, being 
in the axis of the holder and the geometrical axis of the telescope. 
The specifications for the telescope require its line of sight to be 
coincident with its geometrical axis ; thus c, the center of the ball- 
and-socket, lies in the line of sight. The telescope is adjustable 
about c as a center of motion by means of the three thumb screws 
a, b, and c. 























442 


Naval Ordnance 


There is an accessory of the bore sight called the muzzle disk. 
This consists of a circular casting machined to fit snugly in the 
muzzle of the gun with which the bore-sight telescope is to be used. 
It contains a central hole that is -j 1 ^ inch in diameter, if the disk 
is for heavy guns, but is smaller in the disks for short guns. 

544 . The object of bore sighting is to bring the lines of sights 
through the pointers’ telescopes to intersect the axis of the bore 
extended, at the mean range at which it is expected to fire; so that 
with the gun properly bore sighted and with the sights correctly 
set, an accurately aimed shot will hit the “ point of aim.” Of 
course, at ranges shorter than that at which bore sighted, the lines 
of sights will intersect behind the target and at longer ranges, in 
front of the target. 

The target used in bore sighting is a specially prepared screen, 
on which are painted vertical and horizontal lines; the screen is 
properly mounted in a boat and the boat anchored at the desired 
range; this range being the mean range at which it is expected to 
fire. It sometimes happens that suitable objects are available, such 
as prominent marks on shore, beacons, etc., in which case in order 
to save time, the regular target would not be sent out. For long 
range bore sighting, it is customary to anchor the ship at the 
desired range from some land mark or other prominent object, 
and not use the target. 

545 . To bore-sight a broadside gun, we proceed as follows: 

(1) Preliminary to the bore sighting proper, the pointer's - and 
trainer’s telescopes should be examined, cleaned if necessary, 
focused, and all parallax removed. The telescope holders should 
be clean, and telescopes mounted securely in the brackets. The 
sight mount should be clean, work easily, and have no lost motion. 
Set sights so the scales read zero range and 50 deflection. 

(2) Open the breech plug of the gun and lash it open, so as to 
prevent its swinging part way shut and injuring the bore sight. 

(3) Ship the breech disk (breech adapter) in the screw box and 
clamp it rigidly in proper position as indicated by square marks on 
breech and disk. 

(4) Enter the telescope holder in the threaded hole in the 
breech disk, screw home, and then set up tight on the locking 
ring r. 


Naval Gun Sights 


443 


(5) Focus the telescope for distinct vision on an object distant 
not much less than one mile, by moving the eye-piece tube in or 
out. Test for parallax. There should be no parallax, since the 
cross lines of this telescope are permanently fixed in the second 
focal plane of the objective. If, however, parallax does exist, 
another telescope must be used, or the parallax must be removed 
by sacrificing some of the focus. In some cases, it will be neces¬ 
sary to place a piece of paper over the eye piece and punch a pin 
hole through the paper, in order to overcome the effect of the 
parallax, and at the same time secure distinct vision. 

(6) Ship muzzle disk; see that the lip or a line on its periphery 
touches the muzzle face all around. 

(7) By movement of the thumb screws a, b and c (there are 
four of these thumb screws on all of the latest Marks) , direct the 
line of sight of the telescope to the hole in the muzzle disk. Since 
this hole is comparatively close, its image will lie in rear of the 
cross lines and will appear as an indistinct, rather large, round 
bright spot. We would have considerable parallax between the 
cross lines and this image if it were not for the fact that the brass 
cover on the eye end of the telescope has only a small opening, 
and therefore the eye cannot move much off the axis of the 
telescope without losing sight of the image. When the intersection 
of the cross lines appears to lie in the center of the image, see 
that the three (four) thumb screws are set up tight. On a cloudy 
dav, there may not be enough light through the hole in the muzzle 
disk to make the cross lines visible. In this event the lines can be 
seen by means of a portable electric light hung inside the breech 
disk, a little to one side of the telescope. 

(8) Test the adjustment of the bore sight by rotating the muzzle 
disk through 180 0 ; if this makes no difference in the apparent 
position of the intersection of the cross lines on the image, it is 
evident we have placed the line of sight coincident with the axis 

of the bore. 

(9) Remove muzzle disk. 

(10) Man stations at telescopes, officers at trainer’s telescope. 
Pointer coaches trainer crying “ Mark ” when vertical wire is on ; 
the officer notes the error of trainer's vertical wire and by means 
of the adjusting screws on the trainer’s telescope, brings the 
trainer’s vertical wire on with the pointer’s. The procedure is 
repeated for the trainer’s horizontal wire, it being brought on with 


444 


Naval Ordnance 


the pointer's by means of another set of adjusting screws on the 
trainer’s telescope. The pointer’s and trainer’s cross lines are now 
together. 

(11) Officer now mans bore sight, pointer and trainer at regular 
stations. The officer coaches pointer and trainer, officer and 
pointer crying Mark ” when vertical wires are on. By means 
of the sight-setting mechanism, set the sights over in deflection 
until pointer is on with bore sight. This should of course bring 
the trainer on with the bore sight at the same time. Check 
trainer's vertical wire with bore sight vertical wire. The procedure 
is repeated for the horizontal wire, it being brought on with the 
horizontal of the bore sight by setting the sights in range. Both 
the pointer’s and trainer’s cross lines should now check with the 
cross lines of the bore sight. 

(12) When the officer is satisfied that all three sights are 
together, unclamp the range and deflection scales and shift them 
to o range and 50 deflection and clamp tight. Care must be taken 
in shifting the scales, that the scales, only, are shifted, and that 
the sights themselves are not moved. 

(13) Check sights with bore sight to see if sights were moved ; 
if satisfied as to the bore sighting, shift stations, the officer check¬ 
ing both telescopes. This is important, not only that the officer 
may check the pointers, and so serve to eliminate error, but also 
that the pointers may be assured that the telescopes are truly “ on ” 
with the bore sight and hence, any misses in firing cannot be laid 
to poor bore sighting. 

(14) Run the sights up and down; right and left. Set again at 
o and 50; and check again at all stations. 

(15) Put muzzle disk in again and see if the bore-sight line of 
sight is still coincident with the axis of the bore. 

(16) Report to the gunnery officer that the gun is bore sighted 
and ready for inspection. 

(17) After inspection hang a large placard on the gun announc¬ 
ing “ Hands Off—Bore Sighted,” or similar warning, move to 
next gun, or stow gear. 

In the case of the latest periscopic sights, the cross-line lenses 
are made movable, so that step (10) as given above is accomplished 
by moving the cross lines themselves. Step (11) also, may be 
accomplished in the same way with this type of sight, or as stated 
tinder (11). 


Naval Gun Sights 


445 


546 . To bore-sight a turret, the procedure is the same, so far as 
regards the pointers’ sights, as for a broadside gun ; that is, each 
pointer is put on with his respective bore sight. The trainer, 
however, must he placed midway between the guns in case of a 
two-gun turret, and with the middle gun in the case of a three-gun 
turret. 

The details of bringing the cross lines “ on,” shifting the scales, 
etc., are not given since they vary somewhat with each type of 
turret: the principle, however, is the same in all cases and if, this 
principle and the object of bore sighting are clearly understood, 
the details will present no serious difficulties. 

Notes on Care and Handling of Telescopes. 

547 . General directions.—Telescopes should never he dis¬ 
mounted unless it is absolutely necessary, and then only by an 
officer or other person skilled in such work. 

As optical parts of a telescope are not interchangeable, one tele¬ 
scope should be completely reassembled before starting to dis¬ 
assemble another. A line scratched across a joint between two 
parts of a telescope before disassembling, will facilitate reas¬ 
sembling. 

The objective lens is provided with a cover, and it should he 
kept in place at all times when the telescope is not in use; other¬ 
wise the sun will cause the balsam cement to crystallize. 

When possible, telescopes should he stowed in a warm, dry 
place, in boxes provided for them. 

Telescopes should be cleaned with a dry cloth (nothing else), 
and the cloth should never touch the lenses. 

Special care should be taken to prevent injury to pentagonal 
bearings, especially the two lower faces. 

All telescopes are marked “ up ” on the side which should be 
uppermost when shipped. 

Care should he taken that the telescope holders are kept clean 
and smooth. Emery, etc., should never he used for cleaning them. 

Whenever possible, a gun should be bore sighted after shipping 
a telescope. While such telescopes as have non-adjustahle cross 
lines have been carefully inspected to see that the cross line, inter- 
section of all telescopes coincides for a distant object, bore sighting 
should always he resorted to if possible after changing a telescope 
in the telescope holder. 


446 


Naval Ordnance 


Care must be taken that the screw heads of the telescopes are 
not allowed to become rusted. In all future telescopes, these 
exposed parts will be made of Monel metal. Frequent exami¬ 
nation of these should he made to see that they are not slacked 
hack. 

Do not tamper with the bolts which are used to fasten together 
the flanges of the various parts of a prismatic telescope. This 
adjusting can only be done by an experienced man, and requires 
tools not to he had aboard ship. 

548 . Cleaning lenses.—Lenses should be wiped off only when 
necessary, for cleaning destroys the polish, thereby diminishing the 
amount of light passing through. If they are very greasy, a few 
drops of alcohol applied with a brush and then wiped with clean 
chamois skin will usually he sufficient. Handle lenses by the edges. 
Dust can be removed by means of a dry camel's-hair brush. 

Each pointer and trainer should have at hand a piece of chamois 
selvyt, or lens paper, so that he may be able to wipe off the eye¬ 
piece lens in case it becomes covered with moisture, as it does 
sometimes. In no case use waste. A few small holes punched in 
the rubber eye guard will tend to correct this trouble. 

In cleaning the objective lens of a telescope when in place, 
special attention must be given that the objective lens does not 
rotate, as this will cause large errors in the line of collimation. 

Compound lenses are usually cemented together with Canadian 
balsam, which is soluble in alcohol; hence care must be taken that 
too much alcohol is not used in cleaning. 

The above remarks apply to the polished surfaces of prisms as 
well as of lenses. 

In looking through a telescope, it is well to remember that all 
dirt that may be seen very clearly defined must lie in or very near 
to a focal plane. For this reason dirt on the cross-line lens is clear 
and distinct, while that on the objective and eye-piece lens will 
appear as a blur. However, dirt on any lens lessens the amount 
of light that is transmitted to the eye. 

In cleaning cross-line lenses, do not use alcohol, as it removes 
the filling-in material of the etched line. 

549 . Adjusting the illuminator.—The illuminator, when in 
correct adjustment, should render visible only the intersection of 
the cross lines, and not the entire cross line. If the beam of light 


Naval Gun Sights 


447 


should get oft" the intersection, it can be adjusted by means of the 
four set screws at the top of the illuminator, on the outside of the 
telescope. Keep caps on illuminators when not in use. 

550 . Focusing.—The older type of variable-power telescope 
(Mark X) is focused by sliding the inner tube in or out (after 
adjusting the outer tube for desired power) until there is no 
parallax. This position of no parallax marks the position of 
accurate focus. Once focused at, say, 2000 yards, the telescope 
requires no further adjustment for any distance for which it is 
to be used by the same observer. A knurled ring or a lever attach¬ 
ment is provided on later types of variable-power telescopes for 
shifting from one power to the other, while the focusing is done 
by means of the eye piece. In all fixed-power telescopes the focus¬ 
ing is accomplished by means of the eye piece. 

551 . Ray filters.—The ray filters accompanying telescopes are 
to be inserted inside the rubber buffer, close up to the eye lens. 
In some new telescopes, ray filters are included in the telescope 
itself. The dark smoked one is for night use against searchlights, 
while the amber colored one is for day use. 

Alignment of Guns and Sights. 

552 . With a ship on an even keel all guns should elevate and 
depress in a truly vertical plane. Also the sights when run up and 
down independent of the guns should move in a vertical plane. 

Since the installation of the gun and sight mechanisms may be 
imperfect, or, having been accurate, may have become deranged 
through use, it is necessary to check the installation to find and 
correct such derangement of the alignment of guns and sights. 

Bore sighting is of no value if the alignment is out, for, with a 
gun perfectly bore sighted with gun and sight horizontal, if the 
gun elevates in one plane and the sight in another, the planes not 
being parallel, it is obvious that an error will appear, small at 
short ranges, and increasing rapidly with the range. 

553 . In measuring for parallelism of guns, measurements are 
to be taken with the guns resting in the trunnion seats, not raised 
on the knife edges, and, if measurements are taken by trams, they 
should be taken at both breech and muzzle with guns at level and 
at successive angles of elevation and depression by increments of 
about 5 0 . 




448 


Naval Ordnance 


In testing the parallelism of turret guns and sights it is con¬ 
venient to consider three planes of reference, each of which is 
perpendicular to the other two: 

1. The plane containing the axes of the guns when level. This 
plane should contain also the axes of the trunnions, and may, for 
convenience, be called the Horizontal plane. 

2. A plane through the axes of the trunnions perpendicular to 
the horizontal plane. This, for convenience, may be called the 
lateral plane. 

3. A plane through the center line of the turret perpendicular to 
both the lateral and horizontal planes. This plane will be called 
the longitudinal plane. 

It will be noted that these planes are not, strictly speaking, hori¬ 
zontal and vertical unless the ship is on an even keel. 

It is assumed that the turret structure is properly built, the plane 
of the roller path being perpendicular to the longitudinal plane 
through the keel and center line of the ship, and the plane contain¬ 
ing the axes of the guns when level being parallel to the plane of 
the roller path at all positions in revolution of the turret. 

554 . The traces of the longitudinal and horizontal planes are 
projected on a skeleton screen of smooth wide battens secured to 
cross-pieces, placed at a convenient distance from the muzzle of 
the guns; to contain the field of view through the bore sights and 
gun sights, from extreme depression to extreme elevation. (See 
Fig. 104.) This screen must be placed parallel to the “lateral 
plane ” (i. e., vertical), and held securely. The frame holding the 
battens is made heavy enough to permit men to climb upon it to 
plot points. 

The trace of the vertical plane will be the line A-B, and of the 
horizontal plane will be C-D (Fig. 104). 

555 . These lines may be called the vertical and horizontal base 
lines, respectively. 

The conditions for perfect alignment and parallelism of the axes 
of guns are as follows: 

(a) Trunnion seats in deck lugs cylindrical and with axes 
coincident and perpendicular to the longitudinal center line of the 
deck lug. 

(b) Trunnions of slides cylindrical and with axes coincident 
and perpendicular to the axis of the bore of the slide. 


Naval Gun Sichts 


449 


(c) Each deck lug with its longitudinal axis parallel to the 
longitudinal axis of the turret. 

(d) The two deck lugs in one turret so set that the axes of the 
two pairs of trunnion seats are coincident and lie in the lateral and 
horizontal reference planes. 

(e) The two deck lugs in a turret so set that the axes of the 
two guns are equidistant from the longitudinal center line of the 
turret. If all of these conditions are fulfilled and the suns are 
made to revolve about the axes of the trunnions, as in elevating 
and depressing, the planes in which the axes of the guns move 
will be parallel to the vertical reference plane and will intersect 
the plane of the screen in the lines E-F and G-H, parallel to A-B 
(Fig. 104) and equidistant from it. 

In the middle of the flush battens are scribed right lines, as 
shown. These lines should be black upon a white ground and 
should only be sufficiently heavy to be seen through the telescope 
of the bore sight. The distances between the lines E-F and A-B 
and between G-H and A-B are equal to the distance between the 
center line of gun and center line of turret, as shown on the draw¬ 
ings, and are laid ofif on the line C-D before the vertical lines are 
drawn. Care should be taken to have the lines on the vertical 
battens at right angles to that on the horizontal batten C-D. 

556 . The guns are carefully leveled by means of trams,* and 
the battens, secured together, are raised until the line C-D comes 
on the horizontal wire of the bore sight of each gun, and the lines 

* The line C-D represents the horizontal base line, and A-B the vertical 
base line. This is on the assumption that the plane containing the axes of 
the guns when level is the horizontal plane. In fact, the axes of the guns 
when level establish the horizontal plane which is really the fundamental 
plane from which all comparisons are made. 

At shipyards the deck lugs are usually lined up with a mandrel. The 
height of both ends of the axis of the mandrel is measured above the roller 
path by means of a train. This establishes the axis of the mandrel parallel 
to the plane of the roller path within the limit of accuracy expected of 
mechanical measurements. The deck lugs are then lined up with the trun¬ 
nion seats to the mandrel. After the guns are mounted their level position 
is determined by mechanical measurements above the roller path and tram 
marks made near the breeches of the guns on the central girders. This 
establishes the plane of the axes of the guns when level, and when once 
determined as accurately as possible this plane must be the one with which 
all others must be compared in order to give the best results from a gunnery 
point of view. 


30 


45° 


Naval Ordnance 


E-F and G-H coincide with the vertical wires of the bore sights. 
The battens are then secured. 

By means of the bore sight, the axes of the bores of the guns 
are projected upon the screen at successive elevations until the 
height of the screen is reached. Then the guns are brought to 
extreme depression, checking the points of projection previously 
obtained in elevation and at level, and another projection is 
marked at extreme depression. The guns are brought back to level 
and the point of projection in that position checked again in order 


K-E 


c-e^: 


z v 


W 




if 


1 =^= 1 : 




H 


- 


'€ 


B 


Fig. 104. 


f 


4 


I 

s 


3-tr 


IEZEI3- D 


to ascertain if anything has moved. After the points have been 
marked on the screen the guns may be rapidly run up and down a 
number of times with the elevating gear for verification. A line 
connecting all points of projection on the screen is the “ elevation 
line ” and should be a straight line. This line may be actually 
drawn or not, as desired. 

The elevation lines of any pair of turret guns, compared with 
the vertical lines and the horizontal base line ( C-D ) of the screen, 
will indicate the degree of accuracy of the installation, and will 
enable one to measure with a fair degree of precision the error, 







































































































Naval Gun Sights 


45 1 


if any exists. All that is necessary is to measure the lateral 
distance of the points of projection from the vertical lines. If 
each measurement is the same it is evident that the elevation line 
is on or parallel to the vertical base line; otherwise an inclination 
is shown, and must be corrected before the gun will fire accurately. 

557 . To check the motion of the sights the battens K-L, M-N, 
O-P, and A-B are used. These battens have righ J lines in the 
center, and are secured so that K-L is parallel to C-D, and at a 
height above it (in some cases below) equal to the vertical distance 
between the center of the trunnions and the axes of the sights. 
The vertical battens are secured perpendicular to the base line 
C-D and at the horizontal distances of the telescopes from the 
center lines of the guns. These measurements can be obtained 
from the drawings. 

(1) The trainer’s sight.—In a perfect installation of guns and 
sights this sight, when set at zero, should project its axis upon 
the screen at the point b, the point of intersection of the line A-B 
with the line K-L, and when elevated and depressed this point of 
projection should follow the line A-B 

To test installation of trainer's sight: Obtain the “elevation 
line ” in the same manner as for a gun. Mark a " zero point ” on 
this line at a height above C-D equal to the vertical distance between 
the line joining the axes of the guns when level and the axis of the 
trainer’s telescope. Set the sight for zero range and azimuth. 
The line of sight should, for this position of sight, fall upon the 
“ zero point,” and when the sight is made to move up and down 
on its trunnions the line of sight should follow the elevation line 
on the screen. Then turn the sight in azimuth. Project the 
vertical and horizontal wires upon the screen at extreme positions 
of azimuth and at zero azimuth. By means of a straightedge and 
fine-point pencil draw these projections upon the screen. The 
points of intersection of the vertical and horizontal projection 
lines will determine the azimuth line of the sight, which should 
be perpendicular to the elevation line previously obtained, and 
intersect it in the “ zero point.” 

(2) The pointer’s sights.—Referring again to Fig. 104 it will be 
seen that a perfect installation of guns and sights will cause the 
axes of the telescopes to be projected at / and k when the sights are 
at zero range and centrally set in azimuth and the guns level. The 


452 


Naval Ordnance 


axes of the guns when elevated and depressed will follow the 
lines E-F and G-H, and the axes of the telescopes of the sights will 
follow the lines N-M and P-O. It is not strictly necessary, how¬ 
ever, that the axes of the sights when level be projected at / and k. 
A slight lateral deviation from these points will make no material 
difference provided there isr sufficient clearance in the peephole 
of the sight hood for the telescopes of the sights, and provided that 
they be projected on the line K-L. A lateral deviation from k and / 
may be caused by the guns not being installed in accordance with 
the exact measurement from the center line of the turret, as called 
for on the drawing, or by the center of the cam-plate bracket and 
the center of the pivot block being laterally misplaced to an equal 
extent. A lateral deviation due to either of these causes, if 
small, will make no difference in the accuracy of the gun fire. 

(a) The elevation plane of the sight must be parallel to the ele¬ 
vation plane of the gun. 

(b) When the sight is moved in azimuth its axis should move in 
a plane parallel to the horizontal plane through the axis of the 
trunnions of the gun. This may be. called the azimuth plane of 
the sight, and its intersection with the screen may be called the 
azimuth line. 

(c) Starting from a position of level the axis of the gun and 
the axis of the sight must remain parallel through elevation and 
depression. 

558 . Method of testing.—Assuming that the guns are satis¬ 
factorily installed and their elevation lines are E-F and G-H: 
Level the guns with the trams. Starting with the pointer’s sight 
for the right gun, set it for zero range and azimuth and project its 
axis on the line K-L of the screen, as at I. Elevate the gun and 
note whether the line of sight through the axis of the telescope 
follows the line M-N, then gradually depress the sight to level, 
noting whether the line of sight follows down the line. If this 
should be the case, the elevation plane of the sight is parallel to the 
elevation plane of the gun, and the condition stated in paragraph 
557 is satisfied. If, however, the line of sight projects a new line, 
as it is depressed independent of the gun, a faulty sight installation 
is evident. 

Next test the sight by moving it in azimuth. Project the vertical 
and horizontal wires upon the screen at extreme positions of 


Naval Gun Sights 


453 


azimuth and at zero azimuth. An observer at the screen moves 
a square or straight edge until its edge is in the line of projection 
of the horizontal wires as directed by the observer at the telescope, 
when a fine line is drawn to the straightedge by another observer. 
In a similar manner draw the line of projection of the vertical wire. 
Through the points of intersection of the horizontal and vertical 
lines at the positions of observation draw a straight line. This is 
the azimuth line of the sight, and should follow the line K-L unless 
a variable convergence of the guns is shown by their elevation 
lines, in which case the azimuth line should be perpendicular to the 
elevation line of the sight. 

In order to ascertain if the requirement of paragraph 557 (c) 
is fulfilled, project the axis of the gun upon the screen at any 
point, as x, and at the same time note the projection of the axis 
of the sight, as at t. Measure the distance x-e' from C-D and l-t 
from K-L; l-t should be equal to x-e'. 

559 . It has been found by experience in installing pointers’ 
sights that the error most likely to occur is in the elevation plane 
of the sight. This error can be readily detected as follow's: 
Scribe a straight line on a batten, and with the gun level and sight 
at zero range and azimuth, secure the batten at a convenient place 
on deck in a horizontal position, so that the horizontal wire of the 
telescope will be directed at the line on it. Note where the pro¬ 
jection of the vertical wire cuts this line. Elevate the gun suc¬ 
cessively to various degrees of elevation. At each position of ele¬ 
vation of the gun bring the sight down to level, and note the points 
on the horizontal line of the batten found by the intersection with 
it of the projection of the vertical wire of the telescope. If in any 
position of elevation of the gun, the sight set for the corresponding- 
range and brought down to level, the projection of the vertical 
wire is found to cut the line on the batten at the same point as with 
the gun level and sight at zero range, the plane of elevation of the 
sight is parallel to the plane of elevation of the gun. 



CHAPTER XIII. 

FIRING ATTACHMENTS AND GAS-EXPELLING 

DEVICES. 

560 . In U. S. naval guns the term “ firing mechanism is used 
to designate that part of the breech mechanism which directly 
explodes the primer and thus fires the gun. The “ firing attach¬ 
ments ” comprse those appliances, fitted to the gun and mounts, 
which put the firing mechanism in operation. 1 he lock lanyard, 
electric firing battery, wires, terminals, firing key, etc., are attach¬ 
ments. Firing mechanisms are covered in Chapter XI. 

561 . Guns are fired by percussion and by electricity—Per¬ 
cussion primers are used for guns of 3-inch caliber and below, 
while guns of large caliber use combination primers which may be 
fired either by percussion or by electric current. 

For large guns electric firing is considered preferable, percus¬ 
sion firing being used only as an alternative. Electric primers 
shorten the tiring interval, or the time that elapses between the 
instant the gun pointer wills to fire and the instant the projectile 
leaves the muzzle. 1 his interval, which on the average is thiee- 
tenths of a second, has two factors: (1) lhe personal factor 
(which is much the greater), depending on the pointer’s quickness 
and nerve, and (2) the time consumed by the travel of the pro¬ 
jectile along the bore and by the mechanical action of the tiring 
devices. With electric firing, the pointer’s muscles act through 
less distance than when using percussion firing mechanism, and 
the passage of the current is more nearly instantaneous than is 
the action of the lock lanyard, sear, hammer, etc.; and this part, 
at least, of the firing interval is reduced. 

562 . Current for electric firing is furnished by motor gen¬ 
erators or by storage batteries, connections being made so that 
either may be used as desired. The motor generators for this 
purpose, usually two in number, are located in the interior com¬ 
munication room of the ship, and take diiect current fionr the 
ship’s circuit. They deliver alternating current at 125 volts to the 
fire-control switchboard, where the various units of the battery, 


Xaval Ordnance 



/. c., turrets and broadside groups, are cut in or out in accordance 
with orders from the fire-control officer. 

563 . Firing circuit for turret guns.—The wiring diagram for 
the firing circuit of turret guns on a battleship is shown on Plate I. 
It will he seen that direct current for the motor end of the motor 
generators can he taken either from the ship’s mains -or from a 
storage battery discharging at the rate of 50-ampere hours, with 
a voltage of 125. 

The motor generators serve merely to convert direct current 
into alternating current at the same voltage. The latter is led to 
the fire-control switchboard, which is shown to carry four cut-out 
switches, one for each of the four turrets. By closing these 
switches to the right, current is delivered directly to the primary 
coil of a transformer located in each turret. There the voltage is 
“ stepped down ” to 20 volts alternating current at the terminals, 
which is ample for firing the primers in the guns. 

564 . Located in the turret officer’s booth in the turret is a 
selector switch whereby current for firing can he taken either 
from the secondary of the transformer or, in case of failure of 
the motor generator, from a storage battery. Following the dia¬ 
gram, it will be seen that the path of the current leads from this 
switch to the pointer’s firing key at each gun, thence to the turret 
officer’s snap switch (which is closed unless he wishes to cut out 
a gun from firing), then to the gun captain’s ready switch (which 
is closed as soon as the gun is loaded and primed), thence to the 
terminals at the breech of the gun (which make contact as soon 
as the breech is closed and locked), and from this point to the 
primer bridge and thence to ground. It is apparent, therefore, 
that as soon as the gun is loaded, primed, and ready the only break 
in the circuit is the pointer’s key, which is closed when the pointer’s 
sight is “ on ” the target and the signal is given to fire. 

565 . The portion of the firing circuit described so far is 
sufficient to enable the guns to be fired by the pointers. This 
method or system of firing, known as “ pointer fire,” was the only 
one in use until a very few years ago. Within the last few years, 
however, a system of “ director fire ” has been introduced under 
which the guns are laid to a predetermined angle of elevation, and 
the actual sighting and firing is done from a station located usually 
aloft. The remainder of the firing circuit shown on Plate I covers 


CHAPTER XIII. PLATE I 



Wiring Of Check Buzzer, Ex Calibre, And 

DotTER ATTACMrlEMT IN TliRRET© FOR DRILL PURPOSES 
























































































































































































































































































































































































































































































































CHAPTER XIII. 


PLATE II 





1 '-TP OM BATTERY 
'-—TO ETE FIRING TERMINAL 



Fig. 3. —Hand-Wheel and 
Firing-Key, Double Drive. 


SECTION X-X 



Fig. 4. —Hand-Wheel and 
Firing-Key, Double Drive. 


Fig. 5. —Push-Button Type of Firing- 
Handle Used on Two-Handed Drive 
Wheels. 


FIRING-KEYS. 

















































































































































































































































Firing Attachments and Gas-Expelling Devices 457 

this director feature, and consists of the necessary switches and 
leads to the various directorscopes installed on the ship. 

As will be seen from the diagram, directorscopes are located in 
the fire-control tower, the fore top, the main top, and in high 
turrets Nos. 2 and 3. By proper manipulation of switches on the 
fire-control switchboard, any one of these directorscopes can be 
made to control all turrets; or the control may be divided between 
two of them, the fore-top directorscope, for instance, being used 
for turrets 1 and 2, and the main-top directorscope for turrets 
3 and 4. 

When director fire is being used, the four turret switches on 
the fire-control switchboard are thrown to the left. The pointers’ 
keys in the turrets are closed and held in that position, so that as 
soon as the guns are loaded and ready the only break in the circuit 
is the firing key at the directorscope. Firing is done “ on the 
roll,” that is, the directorscope operator closes his key at the 
instant his line of sight is brought on the target by the roll of the 
ship. The guns in the turrets, all laid to the desired angle of 
elevation, fire in salvo as the directorscope key is closed. 

Attention is invited to the fact that all parts of the firing circuit 
receive full voltage except a short section of the leads in the turret. 
This is important, since the long leads to the different director- 
scopes might cause too great a drop in voltage to insure firing all 
primers if there were, for instance, only 20 volts across the motor- 
generator terminals. 

It will be noted that both the fore and main top are provided 
with double leads to the directorscope. This is due to their ex¬ 
posed position. The extra leads are used as a stand-by in case one 
circuit should be cut. 

566 . Plate I shows also the wiring in the turret for dotter gear, 
ex-caliber, and other drill purposes. No special description of 
this material is required, since the diagram indicates clearly the 
various connections. 

567 . The firing circuit for broadside guns, together with the 
lighting circuit, is shown in Fig. 105, which represents a 5-inch 
51-caliber gun and mount with firing attachments. 

In order better to follow the various leads, a diagrammatic lay¬ 
out of the circuit is shown below the mount. It will be seen that 
current for firing niav be taken either from motor generator or 


458 


Naval Ordnance 


battery, the transfer switch being thrown either way as desired. 
From this switch the path of the current leads to the pointer’s 
firing key, then to the breech of the gun where a break in the 
circuit occurs until the breech is fully closed and locked, and thence 
through the primer bridge and primer wall to ground. The other 
end of the circuit is shown grounded at motor generator and 
battery. 



568 . Branching from the lead from battery is shown the light¬ 
ing circuit, which serves to illuminate the cross-wires in the 
pointers’ telescopes, as well as the sight scales and the training 
indicator at the base of the gun mount. It is apparent from the 
diagram that current for lighting is taken only from battery. 
The lamps, which are small and of low voltage, are grounded on 
one side in order to complete the circuit back to the grounded 
battery terminal. 

569 . For director firing of broadside guns, additional leads 
extend to the director tower. There the director is located, pro¬ 
vided with a key for firing all guns of a group or broadside. 
These leads are indicated for convenience in Fig. i, which shows 
the firing circuit of one gun only. Actually the complete wiring 


I 








































CHAPTER XIII. PLATE III. 


I 




Gas Ejector for Broadside Mount. 

















































460 


Naval Ordnance 


diagram would resemble somewhat the diagram for turret guns 
shown on Plate I, where one director can be cut in to fire a number 
of guns. 

Referring to Fig. 105, by closing downward the switch shown 
in the lead from motor generator, the director is cut out, and 
current is provided at the gun for “ pointer fire.” Closing the 
switch upward cuts in the director and puts the circuit in readiness 
for “director fire.” When the latter method of firing is used, it 
of course becomes necessary to close the pointer’s firing key at 
the gun and maintain it in that position, so that the only break 
in the circuit will be at the director firing key. 

570 . In all electric firing chief dependence is placed on the 
motor generator. The battery is used as a stand-by source of 
current in case of failure in the motor-generator line. For director 
fire it is apparent that the battery cannot be utilized at all, since 
its use is confined solely to the gun or turret where it is located, 
whereas director fire involves the firing of several guns in salvo, 
all from the same source of current. 

571 . Firing keys.—In the discussion of firing circuits above, 
reference has been made to the pointer’s firing key, and to the 
directorscope firing key. Plate II shows a number of types of keys 
in use in the naval service. 

The pistol-grip firing key, Plate II, Figs. 1 and 2, is used for 
guns having a one-wheel drive for the elevating gear. Fig. 1 
represents a firing key used for secondary battery guns. It is 
attached to the mount by the hanger shown, and its operation is 
self-evident from the drawing. Fig. 2 is used with certain turret 
guns. The cables enter the butt of the grip, the forward end of 
the grip being attached to apparatus for firing percussion. For 
electric firing, the trigger is pressed in the usual way, thus com¬ 
pleting the circuit through the key. For percussion firing the 
whole grip is pulled upward to operate the percussion mechanism 

Figs. 3 and 4, Plate II, show the firing key for a two-hand drive. 
The two brass rings A and B are insulated from each other, but 
may be connected through the pins C and D by pressing the 
trigger, thus completing the circuit for firing. 

Fig. 5, Plate II, shows the form of firing handle generally used 
on two-hand drive wheels, such as are provided for 5-inch 
51-caliber guns. The firing handle is simply a push button carry- 



CHAPTER XIII. PLATE IV. 



GAS EJECTOR SYSTEM FOR TURRET GUNS. 


















































































































































































































Firing Attachments and Gas-Kxpelling Devices 461 


mg' on its lovvei end a metal bridge to close the gap between the 
insulated firing circuit terminals. In its normal condition it is 
held clear of the terminals by means of a spiral spring. Pressing 
the push button serves to compress this spring and bring the metal 
bridge in contact with the terminals. 

572 . Care of electric firing attachments.—Batteries should be 
frequently tested with a voltmeter, the various parts of the circuit 
with a battery tester, and the circuit as a whole with an ammeter. 
At regular intervals the resistance of each part of the circuit should 
be measured, and the measurements recorded for comparison with 
subsequent readings. Actual tests should also be made by firing 
primers. Unless the electric firing connections are perfect and 
securely held in place, there will be frequent failures to fire, due 
to insufficient current passing through the primer. 

The best test (and the only sure one) of electric firing connec¬ 
tions and battery strength is the firing of primers. The battery 
tester, ammeter, voltmeter, Wheatstone bridge, etc., are mainly 
useful in locating faults. 

573 . The faults most frequently found in the circuit are broken 
wires, or grease or other foreign matter in the connections. The 
firing of the gun will sometimes jar out the plugs, and as it is 
important that this should not occur, they must be well secured. 
Particular care must be taken to see that the primer seat, the 
primer, and all contacts are perfectly clean and free from grease 
or oil. Whenever there is danger of a short circuit, the parts 
should be covered with insulating tape. The failure of the primer 
when using electric firing is generally due to poor contaits. 

Gas-Expelling Apparatus. 

574 . Flare-backs.—The smokeless powder used in the United 
States Navy leaves in the bore, after firing, an inflammable gas 
(carbon monoxide) which sometimes becomes ignited on opening 
the breech plug, causing what is called a “ flare-back ” (see Art. 
25). With bag guns this “ flare-back ” is very dangerous, since 
the powder charges may be ignited by it in loading, as happened 
with disastrous results in the after 12-inch turret of the U. S. S. 
Missouri on April 13, 1904. 

575 . Gas-expelling device.—To guard against flare-backs, an 
air blast is now fitted to all bag guns, in order to blow out through 


462 


Naval Ordnance 


the muzzle the gases remaining in the gun after firing. Plate III 
shows the gas-expelling device fitted to a 5-inch gun, and Plate IV 
shows a similar device for 14-inch and 16-inch turret guns. 

Referring to Plate III, air at about 150 pounds pressure is 
brought from an accumulator through a brass pipe extending up 
through the pedestal. At the top of this pipe, and directly beneath 
the gun, is a stop valve by means of which the air pressure can be 
placed on the gun or shut off as desired. Beyond this valve extends 
a section of flexible metal hose, of length sufficient to allow for the 



recoil of the gun. The after end of this hose is coupled to a 
section of copper piping, which in turn leads to the gas-cjector 
valve located on the breech of the gun. Fig. 106 shows this valve. 

576 . Operation.— 1 he operation of the “ gas-ejector ” valve 
can be readily understood from the figure. The valve seats down¬ 
ward, being held against its seat by a spiral spring and by the air 
pressure in the line. Against the bottom of the valve rests one 
end of the “ valve plunger,’*’ the other end being in contact with 
the cam-shaped “ valve trigger." There is a cam plate on the 














































Firing Attachments and Gas-Fxpelling Devices 463 

breech plug, so located that the first motion of withdrawal of the 
plug in opening brings this plate against tbe valve trigger, revolv¬ 
ing it and thereby pushing the valve plunger upward. This latter 
motion unseats the valve, allowing air to rush past it to a circular 
pipe surrounding the breech of the gun, and thence through holes 
spaced 6o° apart leading to the screw box. As soon, therefore, as 
the breech plug has rotated sufficiently to unseat the “ gas check,’’ 
air is forced out through the muzzle of the gun, taking with it the 
gases lingering in the bore. When the breech is fully opened, and 
the bore is seen to be clear, a member of the gun crew touches the 
trigger of the gas-ejector, thus shutting off the air. During 
firing, air pressure is kept turned on and maintained on the piping 
up to the gas-ejector valve. 

577. Automatic closing valves are installed in air lines to guns 
in exposed parts of the ship such as the upper decks. I he reason 
for this is that the lines are unprotected by armor, and should they 
be pierced the pressure in the accumulators would quickly be lost 
due to escape of air. These valves are so adjusted that the fall 
of pressure due to opening the breech of a gun does not affect 
them, but an abnormal fall, such as that caused by a rupture of the 
air line, causes them to close immediately. 

578. The gas-ejector system for turret guns, shown on Plate 
IV, is similar to that described for broadside guns. Air from the 
accumulators is led to a point overhead near the roof of the turret, 
where an athwartship pipe distributes it to the three guns. It will 
be noted that a different means is provided in this case to allow 
for recoil. Instead of a bight of flexible metal tubing, each gun is 
fitted with a telescoping air line, extending to the breech where 
the gas-ejector valve is located. 

579. Air pressure in turrets.—It is customary to close the 
openings to the turret and maintain the turret chamber under a 
low air pressure from the ship’s ventilating system during firing. 
This is done as an auxiliary, and in addition to the above-described 
gas-expelling device, but never replaces it. 



CHAPTER XIV. 

ARMOR. 

Historical. 

580 . The first publicly recorded proposal to sheath the hulls of 
naval vessels with a metal shield was made by Sir William Con¬ 
greve in The Times in London on February 20, 1805. A similar 
proposal was later made by John Stevens, of 1 loboken, New Jersey, 
in 1812. Nothing came of these proposals for years, but in spite 
of such lack of encouragement, John Stevens and his sons under¬ 
took a series of experiments by which they determined the laws 
of penetration of iron plates by cannon balls and the maximum 
thickness of iron plate necessary to defeat any known gun. In 
1842, Robert L. Stevens, one of John Stevens’ sons, presented the 
results of these experiments, and a new design of a floating battery, 
to a committee of Congress. These experiments of Stevens aroused 
great interest both in America and Europe. In 1841 the French¬ 
man, General Paixhan, also pointed out the necessity of armoring- 
ships, and in 1845 Dupuy de Lome designed an armored frigate 
for the French Government. These proposals resulted in the lay¬ 
ing of the keel of the armored “ Stevens Battery in Hoboken in 
the spring of 1854, followed in a few months by four keels in 
Toulon, and but a few months later by three more in England. 
One of the French floating batteries was fittingly named the 
Congreve. During the following year occurred the first engage¬ 
ment in which armored vessels participated the bombardment of 
the Kinburn forts in the Crimean War by three of the french 
batteries. 

Iron Armor. 

581 . The only metal, practicable and available in suitable quan¬ 
tity, at this period, was iron, wrought or cast, and all experiments 
showed that the wrought iron was far superior, pound for pound, 
to the cast iron, in defeating projectiles. Wrought iron was there¬ 
fore adopted for marine use, and these first ironclads weie pio- 
tected by solid plates between 4 and 5 inches thick backed by 
36 inches of solid wood timbers. 

31 


4^5 


q66 


Naval Ordnance 


The most costly experiments were carried out, especially in 
Europe, where the iron industry was most highly developed, to 
improve the resisting power of wrought iron armor. Tests were 
made of laminated iron plates, with the laminations in contact, 
and with wooden timbers between, but in all cases, single plates 
gave greater resistance per pound of protection. 

During the Civil War most of the armor employed on American 
vessels was laminated wrought iron, but this was necessitated by 
lack of facilities for manufacturing single plates of proper thick¬ 
ness, rather than by any superiority for that type of armor. 

Proposals for the production of face-hardened armor were early 
made. At first these proposals were to face wrought plates with 
cast or chilled iron plates, but as these schemes involved the 
same loss of efficiency as was exhibited by laminated plates, and 
because of the insecurity of the bond between the plates, the 
hard plate failed to secure the full support of the tough back, 
they all failed to compare favorably with single iron plates. But 
as far back as 1863, a Mr. Cotchette proposed, in England, the 
welding of a i-inch blister steel plate to a 3-inch wrought iron 
plate; and later, in I867, Jacob Reese of Pittsburgh, Pa., patented 
a cementation compound which he stated could be used for 
cementing and hardening armor plate. Efforts to carry out these 
proposals failed, for many reasons, primarily because the general 
development of metallurgy was not equal to the task. It should be 
remembered that the Bessemer process of making steel in a con¬ 
verter was developed between 1855 and i860 and that the Siemens- 
Martin process of making steel in an acid open hearth was devel¬ 
oped in France and England a few years later, each process being 
brought to the United States several years after its European 
development. 

Cast iron has been used for armor in land fortifications, where 
weight is of slight importance, but as stated above, it has never 
been applied to naval vessels. The most prominent example of 
cast iron armor is the famous Gruson turret. These turrets were 
made of large iron castings, the exterior surfaces of which were 
chilled by heavy iron chills in the moulds; and were of an oblate- 
spheroidal shape. Due partly to their shape, but also to the fine 
quality of the iron and their great thickness, these turrets were 
considered of great value and were used extensivelv in protecting 


Armor 


467 


European frontiers. The first Gruson turret was tested in 1868 
by the Prussian Government. 

Steel Armor. 

582 . In 1876 gun power and projectile quality had so increased 
that about 22-inches of iron was necessary to accomplish the defeat 
of a projectile from the heaviest cannon, but in that year occurred, 
at Spezia, a trial which revolutionized armor manufacture and 
permitted a reduction in thickness. In these trials a 22-inch mild 
steel, oil-quenched, plate manufactured by the great French firm of 
Schneider et Cie. completely outclassed all its iron competitors. 
This plate is reputed to have contained about .45 per cent carbon 
and to have been hammered down to the required thickness from 
an ingot about seven feet high. The process of manufactme was 
kept secret. This steel plate, while possessing superior ballistic 
resistance, was more prone to breaking up and this difficulty led 
to the next real development, which logically resulted from 
efforts to combine the hardness of steel in the face of a plate with 
the toughness of iron in its back. 1 he steel used in these plates 
was made in Siemens-Martin open-hearth furnaces. 

Compound Armor. 

583 . Thus resulted a new type of armor—the compound type— 
the two principal examples of which were the Wilson-Cammel 
compound plate in which an open-hearth steel face was cast on top 
of a hot wrought iron back plate, and the Ellis-Brown compound 
plate in which a steel face plate was cemented to an iron back 
plate by pouring molten Bessemer steel between them. In both 
these processes, which were English, the plates were rolled after 
compounding. For the next ten years there was no especial devel¬ 
opment in armor manufacture other than minor improvements in 
the technique of manufacture, and great competition and con¬ 
troversy existed as to the relative quality of all steel and com¬ 
pound armor. The all-steel armor was a simple steel of about 
, 0 per cent to .40 per cent carbon, while the steel face of the 
compound armor contained between .50 per cent and .60 per cent 
carbon These two classes of armor, their comparative value de¬ 
pending largely on the skill with which they were made, were 


Naval Ordnance 


468 

approximately 25 per cent superior to their wrought iron prede¬ 
cessor, that is to say—a 10-inch all steel or compound plate would 
resist the same striking energy that a 12.6-inch iron plate would 
withstand. 

Nickel-Steel Armor. 

584 . The next step in advance occurred about 1889 when 
Schneider introduced nickel into all-steel armor, and with the 
advent of nickel-steel armor, began the complete elimination of 
compound armor. The nickel greatly increased the strength and 
toughness of steel. The amount of nickel in the first few examples 
of nickel-steel armor varied between 2 per cent and 5 per cent, 
but finally settled down to about 4 per cent. At about this same 
time oil and water quenching were successfully applied to armor 
plates by Schneider. After forging under a hammer, and anneal¬ 
ing, the plate was heated to a tempering heat and its face was then 
dipped for a short distance in oil, this tempering being followed by 
a low temperature anneal. These improvements resulted in a 
further increase of about 5 per cent in the resistance of armor, 
that is to say, a 10-inch nickel-steel treated plate equalled about 
13 inches of iron. 

It was at this stage of development that the manufacture of 
armor was undertaken in America, by the Bethlehem Iron Com¬ 
pany, under the supervision of Mr. John Fritz, and shortly after¬ 
ward by the Carnegie Steel Company, under Schneider patents, 
and the first deliveries of armor for the old Texas, Maine, Oregon 
etc., consisted of heat-treated nickel steel, containing about .20 
per cent carbon, manganese about .75 per cent, phosphorus and 
sulphur about .025 per cent and nickel 3.25 per cent. 

Harvey Armor. 

585 . In 1890 the next great improvement was begun by the 
introduction of the Harvey process which was first applied to 
armor when a Creusot io-|-inch steel plate was Harveyized at 
the Washington Navy Yard. This process, the invention of H. A. 
Harvey of Newark, N. J., consisted in carburizing or cementing 
the face of a steel plate by heating it and holding it to a very high 
temperature (about that-of molten cast iron ) for from two to 
three weeks, with the face to be hardened in intimate contact with 


Armor 


469 


a bone charcoal or other carbonaceous compound. The result of 
this, treatment was to raise the carbon content of the face to 
between 1 per cent and 1.10 per cent, with a gradual reduction in 
carbon content beneath the surface until the effect of the carburiza¬ 
tion vanished at a depth of about i-inch. Later the plate was oil- 
quenched and then water-quenched, both operations at a uniform 
temperature throughout the plate, the result being that the super- 
carburized face assumed a very hard condition, while the back of 
the plate was toughened. In other words, the face of the plate 
was super-hardened because of its higher carbon content. 

In 1887 Tressider patented, in England, a method of improving 
the chilling of the heated surface of a plate by forcing against it, 
under considerable pressure, a dense spray of fine streams of 
water. This scheme improved on the previous dipping because it 
kept fresh cool water against the heated surface, thus facilitating 
the extraction of heat by eliminating the retarding influence of the 
layer of steam which would otherwise have been formed. This 
water spraying was now combined with the Harvey process and 
we have the nickel steel, cemented, oil-tempered and water- 
sprayed, face-hardened armor known as Harveyized armor and 
sometimes simply Harvey armor. 

A typical chemical analysis of the Harvey armor of this period 
shows the carbon content to have been about .20 per cent, man¬ 
ganese about .60 per cent and nickel about 3.25 per cent to 3.50 per 
cent. 

Shortly after the adoption of the Harvey process it was shown 
that the ballistic quality of a plate could be improved by reforging, 
after cementation. This reforging, giving a reduction of front 
10 to 15 per cent, was conducted at a low temperature and was 
first adopted because it gave more precise regulation of thickness, 
improvement of surface finish and some refining of the structure 
in advance of heat treatment. This process was patented by 
Mr. Corey of the Carnegie Steel Company, under the name 
“ double forging.” 

Harveyized armor immediately established its superiority over 
all other types. The improvement amounted to another 15 per cent 
to 20 per cent increase in resistance, 13 inches of Harvey armor 
equalling about 15.5 inches of nickel-steel armor. 


470 


Naval Ordnance 


Krupp Armor. 

586 . During the eighties, another alloying element, chromium, 
had been introduced into small crucible heats of steel, and the 
resulting alloy was found, when properly heat treated, to possess 
great hardness. Steel makers, in spite of persistent efiforts, failed 
to produce large nickel-chrome steel ingots, or to properly forge 
and treat them when produced, until the great German works, 
Krupp, solved the problem about 1893. 

Krupp also adopted the cementation process for armor, but 
instead of using solid hydrocarbon as in the Harvey process, used 
a gaseous hydrocarbon ; illuminating gas being passed while hot 
across the face of the heated plate. This gaseous cementation has 
been frequently used, but has been gradually superseded by the 
use of solid hydrocarbon. Gaseous cementation was used at 
Bethlehem in 1898 but has since been abandoned and is not now 
used on American armor plates. 

At about the same time Krupp developed a process of deepening 
the hardening on one side of a cemented steel plate. To do this, 
the plate was imbedded in clay or loam, with the cemented side 
exposed, and then the exposed face was subjected to a very hot 
and quick heat. As the heat penetrated gradually, the exposed 
face became much hotter than the back, thus permitting “ dccre- 
mcntal hardening ” by water spraying. A piece of steel heated 
above a certain temperature, will become very hard if quenched in 
water, while its physical properties will be little affected if it is 
quenched when below that temperature. For the sake of conven¬ 
ience, let us call this certain temperature a critical temperature. 
Now as the face of the plate is heated above this critical tempera¬ 
ture, there will always he a plane in the plate at the critical tempera¬ 
ture, and as the heating is continued this plane of critical tempera¬ 
ture will gradually travel inward toward the back, eventually 
reaching the back if the heating is continued long enough. 

However, the plane of critical temperature was only allowed to 
sink between 30 per cent and 40 per cent of the thickness, and 
when that position was reached, the plate was hurriedly with¬ 
drawn from the furnace, put in a spraying pit, and subjected to a 
powerful spray of water, at first on the superheated side and a 
moment later on both sides, the double spraying being done to 
prevent, as much as possible, the warping which a spray on but 
one side would produce. 


Armor 


47 1 


This process, called decremental face hardening, produces a 
very hard face, between 30 P er cent to 4° P e1 ' tent of the plate s 
thickness, and at the same time leaves the other 60 per cent to 
70 per cent of the thickness in its original tough condition. It 
should be specifically noted that this method of hardening depends 
on the decremental heating and does not necessarily involve any 
variations in carbon content. In other words, in this type of face 
hardening, the front portion of the plate is super-hardened because 
of its higher temperature, the depth of the hardening being subject 
to regulation, and greater than the depth of cementation, if desired. 

The process of face hardening, being the final treatment, was, 
of course, applied after the plate had been heat treated to refine the 
grain and produce a fiber in the steel to increase its strength and 

ductility. 

The success of the Krupp process was immediate, and all armor 
manufacturers soon adopted it. In all plates thicker than about 
5 inches, the Krupp armor was about 15 per cent more efficient 
than its immediate predecessor, Harveyized armor; 11.9 inches of 
Krupp being about equal to 13 inches of Harveyized armor. The 
Krupp process was applied to armor for American vessels in 1900. 
Most of the armor made for the past 25 years has been Krupp 
cemented armor. 

During the past 15 years, various slight improvements have 
been made in the technique of manufacture; and it is, as now 
made, possibly 10 per cent better, ballistically, than it was during 

its early use. 

Present Manufacture of Krupp Cemented Armor. 

587 . Carbon being the principal hardening element, the 
natural tendency is to carry the carbon as high as is possible. 1 he 
higher the carbon, however, the more difficult becomes manu¬ 
facture. tears appear in the forging, fibering the plate becomes 
more difficult, and the plate becomes brittle, making it liable to 
cracking and excessive spalling (detaching of surface fragments) 
on ballistic test. The addition of nickel increases the toughness 
of the plate, and permits it, when properly treated, to be fibered; 
while the chromium adds hardness without the extreme brittleness 
which would accompany this hardness if produced solely by carbon. 
The chromium also renders the steel particularly sensitive to 


472 


Naval Ordnance 


heat treatment and thus facilitates the final decremental water 
hardening. 

A typical chemical analysis of a modern Krupp cemented plate 


is as follows: 

Carbon .35 

Nickel . 3.90 

Chrome . 2.00 

Manganese . 35 

Silicon .07 

Phosphorus .025 

Sulphur.020 


In this connection it is interesting to note that when K. C. armor 
was first introduced into America, the plates ran about .27 per cent 
carbon, 3.75 per cent nickel, and 1.75 per cent chromium. The 
increase in carbon and chromium is indicative of the improvement 
ir metallurgical skill and the increased resistance of modern K. C. 
armor which has occurred since its development. 

The modern process of manufacture is briefly as follows: 

t. Melt in a basic open-hearth furnace and pour into an iron 
or sand mould. An ingot for a three-gun turret port plate is about 
42" x 150" x 250" and weighs about 425,000 pounds, while the 
ingot for a belt plate is about 26" X 132" x 200" and weighs about 
200,000 pounds. Dimensions of ingot are varied to suit con¬ 
ditions. (See Plate I.) 

2. Strip while still hot, clean, prepare for forging. 

3. Reheat for forging, and forge under a powerful hydraulic 
press to within about 15 per cent of final thickness; cut off top 
discard of 50 per cent. The forging reduction is about 3 to 1. 
(See Plate II.) 

4. Anneal, to eliminate forging strain, and to put the steel in a 
partially fibrous condition to prevent cracking in cooling. 

5. Super-carburize—this takes from to to 14 days. (See Plate 
III.) 

6. Reheat and reforge to nearly final thickness. 

7. Anneal to prevent cracking while cooling. 

8. Fibering treatment, generally consisting of several treat¬ 
ments to develop the proper physical properties. 

9! Machine to rough dimensions. 

10. Reheat and form to shape. 









CHAPTER XIV. PLATE I 



Armor Ingot, Weight About 400,000 Pounds, Being 
Carried on Two Cranes to be Forged. 



1 


I I 'J 

! 1 

» r 


ft 


4 * - f 










CHAPTER XIV. PLATE II. 



Forging a “ Belt Plate” Under a to,coo-Ton Press. 














CHAPTER XIV. PLATE III. 



Three Plates Loaded on Furnace Bottom Ready to Run in for “ Carburizing. 





CHAPTER XIV. PLATE IV, 



A Side Armor, or “Belt” Plate, oh the “ Spray ” 
After Final Water Hardening. 


» 








Armor 


477 


n. Reheat front face to a temperature above the critical tem¬ 
perature for the depth of chill desired, keeping the back of the 
plate below the critical temperature, and harden under spray. 
(See Plate IV.) 

12. Give a slight heat and rectify curvature. 

13. Finish machine. 

Non-Cemented Armor. 

588 . From the discussion of decremental hardening as applied 
to K. C. armor, it is quite apparent that a plate may he hardened 
without prior cementation. It should be mentioned here that 
the carburized face is much more liable to tearing and cracking 
during forging and bending to shape than is the other portion of 
the plate, a condition which renders the fabrication of thin 
plates more difficult than thick ones. These facts led the Bethle¬ 
hem Steel Company to undertake the manufacture of armor by 
the general Krupp process without cementation. Later the Mid¬ 
vale Steel Company adopted the same idea. Such armor is gen¬ 
erally referred to as Krupp non-cemented or K. N. C. armor. 
In structure, this armor differs appreciably from K. C. armor. 
For instance, there is no super-carburized face, and the chill itself 
is generally harder and somewhat deeper. And there is a further 
difference in chemical composition, in that, while the carbon and 
chrome may be somewhat higher, the nickel may be equal or 
lower, as compared to K. C. armor. Non-cemented armor is fully 
equal, ballistically, to K. C. armor, can in fact be made of supeiior 
ballistic resistance, but it has an unfortunate tendency to spalling, 
both on projectile impact, and even from internal strain. It was 
this tendency to spalling which led to the abandonment of the 
process after a few years of use. A typical analysis shows carbon 
as high as .50 per cent, with nickel at 3.5 per cent and chiomium at 
2.30 per cent to 2.50 per cent. 

Class A Armor. 

589 . The general term Class A armor is applied, in the Ameii- 
can Navy, to all face-hardened armor, whether Krupp cemented 
or Krupp non-cemented. 


4/8 


Naval Ordnance 


Summary. 

590 . It will be seen from the preceding review that each change 
in armor has added something, and that modern armor contains 
all the essentials of each successive product. First, for marine 
use, we had the simple wrought-iron armor, which was later devel¬ 
oped into compound iron-steel armor. Then all-steel armor dis¬ 
placed the compound armor, and was in turn improved by the 
addition of nickel. Next we have a return to the hard face prin¬ 
ciple, hut with homogeneous structure, in the application of 
Harveyizing. And finally we have the introduction of chromium 
and the development of decremental hardening as applied to both 
cemented and non-cemented plates. 

The manufacture of efficient armor requires not only a high 
quality of metallurgical skill, but also most expensive tools and 
equipment. The various improvements in its quality and manu¬ 
facture have, therefore, been as closely related to the inventions 
and discoveries of metallurgy, as to the commercial growth of the 
general steel industry. A knowledge of the nature and dates of 
the various stages in its development, therefore, gives the ordnance 
student an excellent picture of the evolution of the use of iron 
and steel. Frequently the demands of the ordnance engineer have 
caused developments in metallurgy which have had far-reaching 
commercial application, hut more frequently the general improve¬ 
ments made by the metallurgical engineer and chemist have opened 
new vistas to the designers'of ordnance. 

Inspection and Test. 

591 . All during manufacture the processes are watched to insure 
uniformity in procedure and product. Chemical analyses are made 
to insure homogeneity in the metal, and test specimens are taken 
out of the ends of the plates to determine the uniformity of the 
physical properties. Finally, after water hardening, fragments 
called coupons are broken off diagonally opposite corners, in order 
that a microscopical examination may be made of the internal 
structure. (See Plate V.) 

Plates are arranged in “ groups,’’ each containing from 6oo to 
1200 tons, and after water hardening a plate is selected from 
the group, sent to the proving ground, and there tested ballistically. 
If successful, the group is passed to completion, if unsuccessful, 


CHAPTER XIV. PLATE V, 




Coupon from io-inch Plate. Broken Cold Under Press. 













4 <Ho 


Naval Ordnance 


the group is rejected for retreatment. The ballistic test consists, 
at present, in subjecting the plate to the normal impact of two 
major caliber A. P. projectiles at specified velocities, the velocity 
depending on the gauge of the plate and size of the projectile. 
This relation will be discussed under the heading of “ penetration.’’ 

The Ballistic Test. 

592 . In testing and experimenting with armor, great energies 
must be absorbed. For instance, a 16-inch projectile striking 
normally at 2000 f. s. delivers about 60.000 foot-tons. Assuming 
that the plate is 10 ft. x 20ft. x 15 in., that gives about 300 foot-tons 
per square foot of plate area, or about 1100 foot-tons per ton of 
plate. The structure to which the plate is attached must, there¬ 
fore, be of great strength. Such structures are called " plate- 
butts.” (See Chapter XVII, Plate II.) Similar structures used 
for testing the action of projectiles against plates are called 
“ projectile-butts.” 

Particular attention must be given in conducting all impact tests 
to eliminate, so far as is possible, all movement of the attacked 
plate, or in other words, to preserve the rigidity of the structure as 
a whole. This is particularly true when plates are attacked at other 
angles than normal, for in such cases there may be most powerful 
end thrusts, which, if uncontrolled, will permit end movement and 
therefore subject the projectile to uncontrolled and unknown 
“ whip,” thereby vitiating the value of the test. Plate VI shows 
an armor plate after undergoing test. 

The routine ballistic test has been mentioned previously. The 
two shots required are for the purpose of determining whether the 
manufacturer's current manufacturing methods in general, and the 
group represented, in particular, are up to the required standard. 
That condition having been established, and the group’s accept¬ 
ability settled, it is customary to attack the plate with one or two 
additional shots to determine its precise “ ballistic limit.” To deter¬ 
mine this ballistic limit the velocity of impact is increased until 
penetration is just or nearly secured. Experienced personnel can, 
with ordinary armor, generally secure this result (after two 
ballistic test shots) in two more shots, and sometimes even with 
one shot. 


CHAPTER XIV. PLATE VI 



A Ballistic Test Plate. 












482 


Naval Ordnance 


In experimenting with and testing armor it is the ballistic limit 
which is the significant figure. How it is expressed will be shown 
later. But it is easily seen that by always working for it. a record 
can easily be compiled, in time, which will show, not only the 
general average of performance, but also the peak of performance. 
And by always carefully investigating the plates which give the 
greatest resistance, the general standards may be raised. 

Penetration. 

593 . Great discussion took place in the early days of ship armor 
as to whether armor could best be defeated by “ racking ” or 
“ punching.” Racking was produced by very large solid ball shot 
at low velocity and resulted in knocking plates off the ship’s side, 
thus exposing her vitals; and punching was produced by elon¬ 
gated projectiles, at high velocity, and resulted in perforation and 
the immediate attack of the ship’s vitals. This discussion was 
settled during our Civil War very emphatically, and later in the 
Huascar-Cochrane and Blanco Encalado engagement; for the 
shots which secured decisive effects, practically without exception, 
were piercing shots. This discussion finds its echo in more recent 
controversies concerning the relative merits of armor-piercing 
and high-capacity projectiles. Here again war decided em¬ 
phatically, for in the World War it was conclusively shown that 
the decisive hits were those made by armor-piercing projectiles. 

594 . The principal function of armor is, therefore, to prevent, 
in so far as possible, the penetration of a projectile into a ship. 
But the “ racking ” effect cannot be neglected. This is at present, 
primarily a matter of securing—but the use of 16-inch, and even 
larger guns, with their projectiles of great weight; the demand 
for increased speed and consequent sacrifice in protection ; and 
the probable obliquity of impact in action, are gradually forcing 
attention back to tbe “ racking ” or “ smashing ” attack. 

595 . The penetration of a pointed projectile into a homogeneous 
or simple plate was very accurately expressed, in the early days of 
armor, by various empirical formulas. The one which has sur¬ 
vived the various developments, and is still the basis of armor 
calculation, is that of a Frenchman, J. deMarre. 


Armor 


483 


This formula, as used in the last eighties, as applied to the 
penetration of cylindrical projectiles with ogival heads into plain 
wrought iron, is as follows: 


e 65 = 


w 50 v 


log 1 2.9616 d M 


(A) 


or in the shape in which it is generally used: 

log V — 2.9616 + .75 log d -(- .65 log c — .50 log w, 

in which 

e — penetration in inches. 
d — diameter of projectile in inches. 
w — weight of projectile in pounds. 

V — velocity of projectile in foot-seconds. 

Problem I .—How far will a 10-inch 500-pound projectile pene¬ 
trate into a wrought-iron plate at a striking velocity of 1772 f. s. ? 
Answer: 23.1 inches. 

596 . Subsequent to the adoption of nickel-steel armor, the 
formula was revised, and when applying to that material we use it 
in the following form: 

log V = 3.00945 + .75 log d + .70 log e — .50 log w. (B) 
Problem //.—How far will a 10-inch 500-pound projectile pene¬ 
trate into a nickel-steel plate at a striking velocity of 1772 f. s. ? 
Ansiver: 15.77 inches. 

Problem III .—What is the ratio between penetration in wrought 
iron and nickel-steel? 


Answer: 


iron ^ _ nickel-steel 

= 1.4647 or - ; -- .6827. 


nickel-steel " iron 

In nickel-steel armor, the projectile encounters a homogeneous 
material and therefore a more or less constant resistance. In face- 
hardened armor the projectile encounters media of varying hard¬ 
ness and strength, and its retardation follows laws which can be 
but imperfectly stated. For purposes of comparison, therefore, 
the limit of resistance of face-hardened plates is generally referred 
to a basis of penetration of nickel-steel. 

597 . Upon the introduction of face-hardened armor, therefore, 
the DeMarre formula was modified by introducing a coefficient of 
reduction (K), thus: 


( K) *■" = 


V 


log- 1 3.00945 d lh 
or in the form in which it is used : 

log V- 3.00945 + .75 log d -I- .70 log e — .50 log W + log K . (C) 





484 


Naval Ordnance 


Problem IV. —Assuming K as 1.23 for a particular Class A 
plate, what would be the penetration of a 6-inch A. P. projectile 
weighing 105 pounds at 1836 f. s. striking velocity? 

Answer: 7 inches. 

598 . The most useful and frequent application of the formula 
in this connection is, however, to determine the comparative value 
of plates. If we determine by test, the velocity at which a plate 
just resists penetration or just permits penetration by a particular 
projectile, we may consider the coefficient of reduction, mentioned 
above, as a factor of performance, and then, solve the equation to 
determine the factor of performance. The formula then becomes : 

log K = log V - .75 log d - .70 log e + .50 log w - 3.00945. (D) 

599 . This formula is very useful for normal impacts, but like 
all empirical formula, it has its limitations. It is most accurate 
and useful at striking velocities between 1400 f. s. and 2000 f. s. 
and when the ratio between the diameter of the projectile and 
thickness of plate lies between 1.2 and 0.7; but it is liable to give 
erratic or misleading results when those limits are exceeded. 
And, in addition, the formula assumes similarity of projectile 
quality and penetrative ability. 

Problem V. —Find the maximum factor of performance, or as 
it is generally expressed, the DeMarre coefficient, of a particular 
K. C., 12-inch plate. 

Solution: Let us assume that our recent experience in testing 
armor has shown that the average DeMarre coefficient is about 
1.16. Experience has also dictated that the DeMarre coefficient of 
a plate, can be most reliably and usefully determined when even 
caliber projectiles are used. (By even caliber, we mean that the 
caliber of the attacking gun and thickness of the plate are the 
same.) We therefore decide to use the 12-inch gun, with an 
870-pound projectile, with which to secure our data. 

Solve formula (C), for the conditions given, and decided upon, 
and we get 1463 f. s. We fire a shot at this velocity and learn 
that the projectile penetrated by a small margin, the amount of 
margin being approximated by its travel after penetration. 

We fire a second shot at a velocity of 1400 f. s. and the pro¬ 
jectile fails to penetrate, but from the looks of the hole it is cer¬ 
tain that a slightly greater velocity would have caused penetration. 
We conclude that a velocity of 1420 f. s. would have just caused 


Armor 


4^5 


penetration and using this figure we solve formula (I)) and 
determine: 

The maximum factor of performance of this plate is 1.12, or in 
other words, that its limit of resistance is represented by a 
DeMarre coefficient of 1.1165. 

Problem VI .—A 14-inch Class A plate was attacked as follows: 
First shot, 12-inch 870-pound projectile, at 1500 f. s. Pene¬ 
tration, 10 inches. 

S'econd shot, similar projectile at 1545 s - Penetration, 13 
inches. 

Third shot, similar projectile at 1590 f. s. Penetration complete. 
What DeMarre coefficient expresses the limit of resistance of 
plate ? 

Answer: About 1.108 at V— 1570 f. s. 

Problem VII .—A 13-inch Harveyized nickel-steel plate was just 
defeated by a 10-inch 500-pound projectile, at a velocity of 1620 
f. s.; while a 12-inch K. C. plate was just defeated by a similar 
projectile at a velocity of 1685 f. s. What is the relative value of 
the two plates ? 

Answer: Harvey plate is to Krupp plate as 1 is to 1.216. 

Oblique Attack. 

600 . It will be accepted, without proof, that by inclining a plate 
to the line of fire its resisting power is enhanced. We may state 
this in two ways: first, as the angle of obliquity increases, with a 
given plate, the projectile will require a greater velocity to pene¬ 
trate; or, as the angle of obliquity increases, there is a decrease 
in thickness of the plate necessary to defeat a given projectile, at 
a constant velocity. 

The angle of obliquity is the angle between the line of fire and 
the normal to the face of the plate at the point of impact. 

601 . Many efforts have been made to express the relationships 
existing between normal penetration and oblique penetration, so 
far with but partial success. 

Considerable experimentation has shown that while the ratio 
is obscure throughout the entire quadrant (normal to o°) a much 
clearer relation is shown in each of the three sectors, from normal 
to 6o°, from 6o° to 30° and from 30° to o°. That is to say, having 
determined the velocity necessary to defeat a plate at say 45°, the 
velocity to defeat the plate at angles of obliquity between 60 and 


486 


Xaval Ordnance 


30° may be fairly accurately determined by applying a given ratio 
to that velocity. Or, having determined the defeating velocity of 
a plate, with given projectile, at 15 0 , one may predict, with 
reasonable accuracy, the defeating velocity with that projectile and 
plate at angles between normal and 30°. 

602 . It should be borne in mind that there is a real difference in 
the action of the plate and projectile in the three sectors mentioned 
above, the change from sector to sector being gradual. 

However, in the most oblique sector, that from 30° to o°, there 
is a decided difference from the other two for in this sector we are 
dealing with the glancing blow in most pronounced form. This 
difference has given rise to a specific class of armor, designed to 
care for this particular condition. 

603 . Experiments have indicated that the velocity necessary to 
defeat a plate varies about as the fourth power of the secant of 
the angle of obliquity. 

Thus, if V — velocity which will just penetrate at normal and 

V' = velocity which will just penetrate at an oblique 
impact of 0 °, 

we have 

V'=V sec 1 0 = — ^-r-n • (E) 

cos 4 6 

604 . This ratio can be reduced to figures, and when so used is 
generally referred to as an “ angle multiplier.” In order to plan 
an attack on a given plate we fix the normal velocity by the 
DeMarre formula (D) and apply the angle multiplier ” as deter¬ 
mined by the above formula (E) to fix the velocity for the speci¬ 
fied test. 

In the sector from normal to 6o° the ratio is more or less 
correct, while in the middle sector, from 6o° to 30° it can be used 
as a basis of comparison. 

Or. if we know with reasonable certainty the velocity necessary 
to effect penetration at a given angle on a particular plate and 
desire to calculate the velocity required to penetrate a plate of 
different thickness and equal ballistic resistance we would divide 
the velocity by the angle multiplier, then use the DeMarre formula 
(D) to calculate the relative velocities on the basis of normal 
impact, and finally secure our desired result by applying the 
“ angle multiplier ” to our calculated normal velocity. 



Armor 


487 


605 . These calculations can be facilitated by mathematically 
combining formulas (D) and (E), which gives us the following: 

log V— 3.00945-f.75 log d + .70 log <? — .50 log 4 log cos 0, (F) 

where 6 — angle of obliquity (between line of fire and normal). 

In our discussions of Class A armor penetration and the use of 
the DeMarre formula, we have thus touched on two special 
factors: the factor of performance for normal impact, and the 
angle multiplier for oblique impact. In experimental work it is 
well to keep these two factors separate and distinct, and to plan 
and work out our problems so that the ratios between different 
plates are kept related to these two separate factors. 

Class “ B ” or Deck Armor. 

606 . Prior to the introduction of compound or face-hardened 
armor all armor aboard ship was the same. It early became appar¬ 
ent that face-hardened armor was less effective against glanc¬ 
ing impacts of considerable obliquity than was an equal weight 
of homogeneous armor. The advent of K. L. armor further 
strengthened this conviction. The development of a special armor 
to resist glancing blows dates, therefore, from the introduction of 
face-hardened armor. It is apparent, in the glancing blow, that a 
hard face is unnecessary, and that what is desired must be a com¬ 
bination of the highest strength and ductility, in order that the 
projectile may be gradually deflected, hi other words, against 
this attack, we permit the armor to give under the blow, thereby 
spreading the effect, while the projectile slides along the trough it 
creates, thus further spreading the effect, and finally is completely 
deflected. 

607 . In a normal impact the blow is largely limited to a circular 
area with a diameter of about three calibers (see Plate VI), while 
in a glancing impact, at say 15 0 , the effect of the blow is taken on 
an area about three calibers wide and about four to five calibers 
long. 

608 . Armor to resist the glancing blow is now called “ Class B 
Armor ” in the American Navy, but it is also referred to as deck 
armor, horizontal armor, and special-treatment steel. 

609 . Nickel-steel continued to be used for horizontal armor for 
many years, and was accepted on physical properties as deter- 


488 


Naval Ordnance 


mined by tensile-pull specimens, until about 1909 when several 
developments took place. About that time the Carnegie Steel 
Company applied the newly developed nickel-chrome-vanadium 
alloy-steel to this armor and the change in composition and in¬ 
creased metallurgical skill enabled its resisting powers to he con¬ 
siderably increased. In that year the ballistic test of horizontal 
armor, for protective decks, turret tops, etc., began. These tests 
were at 81 0 obliquity. 

610 . About 1914 the use of vanadium was discontinued as it 
was found that more uniform plates could then be made. 

At present, a nickel-chrome steel of approximately the same 
chemical composition as Class A armor is used, that is, carbon 
about .30 per cent, nickel about 3.85 per cent, and chrome about 
1.85 per cent. 

Class B armor, when less than 4 inches thick, is rolled in a mill 
instead of being forged, but above that thickness it is forged, as 
rolling thick plates is believed to work the plate less uniformly 
than forging, a condition which would, of course, tend to reduce 
ballistic resistance. Above 4 inches, if the plates are large, forg¬ 
ing must be resorted to as there are no American rolling mills 
equipped to handle the required ingots. 

The treatment is quite different from that of K. C. armor, for 
the desideratum is to secure great strength and ductility. Thus 
tensile test specimens frequently show an “ ultimate strength ” as 
high as 115,000 pounds per square inch with an “elongation ” in 
two inches of 23 per cent and “ reduction in area ” of 65 per cent. 

Ballistic Test. 

611 . Class B armor is handled in “ groups ” as is Class A armor, 
and each ballistic plate is subjected to the impact of a major-caliber 
projectile at angles of obliquity, depending on the thickness of the 
plate, from 8o° up to about 55°. 

Comparisons between plates and calculations as to suitability 
of plates to meet certain conditions may be approximated, for 
plates between approximately 4 inches and 9 inches, by the follow¬ 
ing mathematical methods. These are not applicable to plates 
less than 4 inches thick. 

In the first plate the resolved normal energy is used to represent 
the force acting. 


Armor 




489 


The energy of a projectile in foot-tons is represented by the 
expression 

wv 2 


E = iMv 2 = 


2 x 32.16x2240 ’ 


while the resolved normal energy is represented by the expression 

p, _ wv 2 cos- 0 

I44°77 

where 

E = total energy in foot-tons. 

Ii' = resolved normal energy in foot-tons. 
w = weight of projectile in pounds. 

V — velocity of projectile in foot-seconds. 

0 = angle of obliquity (from normal). 



As a rule the angle of attack, or the complement of the angle of 
obliquity, is taken in degrees as about four times the plate thick¬ 
ness in inches and the caliber of tbe projectile is taken as about 
two and a half times the plate thickness for 4-inch plates and 
twice the plate thickness for heavier plates. 

Within the limits just stated the minimum thickness of plate 
to withstand attack may be expressed as follows: 

156c 2 , (G) 

where 

E' — resolved normal energy in foot-tons. 
e — thickness of plate. 


Combining the two expressions just given, we get 


i 5 6c== ”^ co$ ^ , 

144077 


or 


t/_ 7.35172+ 2 log e — log w — 2 log cos 6 

lOg v - “ 


(H) 


Using this formula, striking velocities may be calculated upon 
which to base a test, with a reasonable certainty that the limit of 
the plate may be approximately reached. 

Problem VIIE —Determine the condition under which the first 
shot shall be fired to determine the limit of a 5^-inch Class B plate. 

Answer: Select, 14-inch gun, projectile weighing 1400 pounds. 

Select, 68° as the angle of obliquity. 

Then V- 1860.3 f. s. 







490 


Naval Ordnance 


The above mathematical process is by no means thoroughly 
reliable, but it may be useful in handling comparative tests. 


Armor Bolts and Securing. 

612 . References made heretofore in regard to armor butts, 
testing, and inclined armor, and a consideration of the enormous 
forces concerned on impact, point out the necessity of properly 
securing armor to the structure of the ship. Experiment only 


CANVASS SOAKED 
IN THICK KED LEAD 


STEEL WASHERS 
IN HALVES 


BACKING 


SIZE OF BOLT 
DETERMINED BY 
THIS DIMENSION 


NICKEL STEEL BOLT 


NICKEL STEEL NUT 



RED LEAD JOINT 


STEEL WASHEB 


BACKING PLATE 
OR HULL 


SOFT RUBBER 
WASHER 

OAKUM 


ARMOR 


Fig. 107.—Watertight Bolt. 


increases the importance to be attached to the subject. Many 
experiments have conclusively shown that all flexible mountings,, 
such as steel springs, rubber buffers, etc., designed to absorb 
energy, cushion the plate, or extend the time interval in which 
the plate can act, are not only of no value, but are, on the contrary, 
a source of actual weakness. 

Class A armor is bolted to the skin of the ship, or to her framing 
and bulkheads, with heavy bolts of special design called “ armor 
bolts,” the plates being placed against a backing of fitted timber 
or hydraulic cement. (See Fig. 107.) 
























Armor 


491 



Fl0 10 g_ Butt, Main Belt, Showing Key. External Class A Armor. 



■p IC toq.—Angle Joint, Showing Key. External Class A Armor. 













49 2 


Naval Ordnance 


In addition to bolting, abutting edges are keyed together with 
a double tongue and groove key which is driven in endwise; and 
plates which meet at angles are rabbeted, or keyed. (See Figs. 
108 and 109.) 

Class A armor is seldom considered as a factor in the strength 
of the ship’s structure. 

Class B or deck armor, however, is generally worked into the 
structure, and in deck armor, except with the heaviest plates, is 
riveted in as in ordinary plating. The heaviest plates in decks and 
the tops of turrets and conning towers are secured with bolts, 
on the same general plan as are Class A plates. No backing 
is, of course, used. 

613 . Armor bolts are so spaced as to provide one bolt for every 
five square feet of surface, so far as the framing behind armor 
will permit, except in the case of 3-inch armor, for which one bolt 
is used for about six square feet of surface. 

Armor bolts are made from good quality nickel steel (about 
3.5 per cent nickel), the requirement being strength and ductility, 
for the bolt must be strong enough to hold the plate and should 
possess such ductility as will permit the plate to warp and spring 
under projectile impact without cracking. 

Experiments and Conclusions. 

614 . The development of armor has only been secured by con¬ 
tinual and costly experimentation, practically all of which has been 
productive of good. 

Besides producing the armor which we use to-day, these experi¬ 
ments have demonstrated the following general principles: 

(1) That, to be efficient, armor must be homogeneous as to 
mass, so as to concentrate the resistance. 

(2) That armor should be rigidly attached to its supporting 
structure. 

(3) That inclined armor, designed to deflect the projectile upon 
impact is, for purposes of protection, about equal to vertical 
armor of equal weight, when the angle of inclination is greater 
than the biting angle of the projectile; but when the angle of 
inclination is not greater than the biting angle, vertical armor of 
equal weight is more efficient. The introduction of the cap has not 
altered this principle. 


Armor 


493 


Arrangement and Distribution of Armor. 

615 . Armor serves two purposes: hirst, protection for the 
water-tight integrity and interior mechanism of the vessel; and 
second, protection of the personnel. 

This protection is afforded to as great an extent as possible by 
the armor belt, extending the whole length of the ship, the case¬ 
mate armor, the protective deck, turrets, barbettes, gun shields, 

and conning towers. , 

The arrangement and distribution of armor on ships of various 
classes is described in works on naval construction, to which 
the reader is referred for details. 

Light Armor. 

616 . During the World War, insistent demand resulted in the 
development of a third type of armor, generally called light armor. 
This type is used for the protection against small-arms fire, of the 
vital parts of soldiers’ bodies, machine guns and light artillery, 
trains, automobiles, vital parts and personnel of aircraft, and its 
use is being extended to providing protection from aircraft attach, 

for the exposed personnel aboard ship. 

In some of these uses, as for instance body armor, and aircratt 
armor, the greatest possible protection must be secured with the 
least weight, a condition imposed on all armor, in fact, but most 
accentuated in these uses. In this type of armor the metallurgist 
can use his utmost skill, for the mass is small. One might almost 
say that laboratory methods may be followed. 1 his branch of t ic 
art is too young to permit of classification. So far no attempt 
has been made to face harden, for the thickness varies between 
K of an inch for body armor, up to ± of an inch for aircraft armor, 
and then jumps up to about an inch for such heavy vchic es as 

tanks and trains. 

Generally speaking, this armor resembles Class B armor,, al¬ 
though many special and expensive alloy steels are being tried. 
We find the so-called, high-silicon, high-manganese, vanadium, 
zirconium, cobalt, chrome and nickel alloys in various proportions 
and combinations, and plates have been tested giving, with fan- 
ductility, ultimate strengths per square inch as high as 250,000 
pounds. One fact seems to stand out-« desirable as ts strength- 

good ductility is a necessity. 




CHAPTER XV. 

PROJECTILES. 

Form.. 

617 . All projectiles, intended for use in cannon at long range, 
are similar in shape, irrespective of their size and the purpose for 
which they are intended. The shape now in current use is the 
result of an evolution which dates back to the first part of the 
fourteenth century, when cannon are first known to have been in 
existence in Europe. From that time until 1520 the principal 
projectiles were solid spherical stone balls and iron-headed darts. 
It is really astonishing to realize that guns of 25-inch caliber, firing 
a stone ball weighing about 700 pounds, were made as far back 
as about 1382! 

While the casting of iron was known in the fourteenth century 
it required many years and experiments to apply the art to pro¬ 
jectile manufacture. With solid spherical projectiles the sectional 
density can only be varied by varying the material in the projectile, 
and it is quite probable that the development of iron projectiles was 
retarded by the inability of the guns to stand such heavy projectiles 
without bursting. Gradually, however, it grew into use and in the 
early half of the sixteenth century cast iron became the principal 
material used in projectile manufacture. Shortly after this the 
hollow ball, or shell, was introduced. 

Few developments of importance occurred thereafter until 
1854, when the application of rifling to cannon began. That devel¬ 
opment had an immediate and pronounced effect on projectile 
design. The rotation of the projectile permitted its elongation ; 
thereby securing increased range by reducing the head resistance 
for the same mass; increasing the accuracy of flight; increasing 
its penetrative ability; and increasing the mass of the projectile 
which a given gun could accommodate, or in more technical terms, 
the sectional density of the projectile. 

Length. 

618 . At first projectiles were but slightly elongated, but each 
increase in the power of the gun and the efficiency of the rotative 

495 


\ 


496 


Naval Ordnance 


mechanism was followed by a corresponding increase in the rela¬ 
tive length of the projectile. 

During the Spanish War our projectiles were between 2.5 and 
3.0 calibers long, and during the World War their length had 
increased until 3.5 calibers was considered a medium length and 
4.5 calibers was frequently and successfully used, with a few 
instances of even longer ones. 

It is easily seen, without special mathematical demonstration, 
that as the length of the projectile is increased, its speed of rota¬ 
tion must be correspondingly increased. The problem of lengthen¬ 
ing a projectile is, therefore, not a simple one. 

Form of Forward End. 

619 . Early in this development many experiments were con¬ 
ducted to determine the proper shape for the extremities. The 
form adopted for the front end was that known as the ogive, which 
is generated by the revolution of the arc of a circle around a 
chord, the chord being the axis of the projectile, the versine of 
the arc being the semi-diameter of the projectile, and the sine of 
the arc being the length of the ogive. The shape of this ogive is 
generally expressed by stating its radius in terms of calibers. At 
the present time the majority of the U. S. Naval projectiles have 
ogivals of 7 calibers radius. Frequently the ogival shape is se¬ 
cured by the combination of several arcs of different radii. In 
recent years also, the ogival shape has been occasionally abandoned 
in favor of a conical shape, or partially conical shape, as that form 
lends itself with greater facility to mechanical processes. 

With proper rotation, it is desirable to keep the center of gravity 
of the projectile to the rear of, or in the immediate vicinity of, 
the center of form, particularly in long projectiles. As piercing 
projectiles require a blunt and solid nose for penetrative ability, 
the amount of metal in the forward end must be great. Also a fine 
forward form is conducive to long range. To reconcile these two 
opposing yet necessary qualities it has been advantageous to adopt 
light nose pieces, wind shields, or false ogives, all of which names 
are more or less synonymous. Several types of these are shown in 
the following sketches, and in the plate of projectile designs. 

I'lie following table shows, for a 6-inch projectile, the effect 
on the range of varying the radius of the ogive; the muzzle 


Projectiles 


497 


velocity, angle of elevation, weight of the projectile, and form of 
rear being common for all shots. 


Radius of ogive 

Length of projectile 

Effective ran 

in calibers. 

in calibers. 

in yards. 

2-5 

Oj 

0 

0 

9,083 

5-0 

3-37 

10,549 

6.0 

3-50 

10,921 

7.0 

362 

11,285 


The percentage of increased range, of the finer form over the 
blunter form, increases with the angle of elevation; that is to say, 
the improvement becomes greater as tbe range increases. 



STREAM LINE GERMAN S-fl INCH H E. PROJECTILE 

LENSTH = 4-.T CALIBERS 



Fig. iio.—American 6-Inch Experimental H. E. Projectile. 
Length = 5.2 Calibers. 


Form of After End. 

620 . Variations in the shape of the rear end of the projectile 
have not been as prolific of beneficial results as might be expected 
from the preceding discussion of the forward end. All projectiles 
have the corner of the base turned to a small radius and for many 
years that shape was standard. Practically all U. S. Naval pro¬ 
jectiles have this rounded corner, the radius varying from .375-inch 
for large projectiles down to a mere touch of the file on the corner 
of the small ones. 


33 






















































49§ 


Naval Ordnance 


Frequent firings have,however, shown that increases in range can 
be secured by shaping the base to a finer form than a mere round¬ 
ing of the corner. This scheme is generally referred to by naval 
ordnance engineers as boat-tailing, an expressive but peculiar term. 
But the deterrent fact is, that while comparatively small increases 
in range may be secured, they are generally accompanied by loss 
of accuracy! This is generally assumed to be caused by a flip or 
unequal side slap given to the rear of the projectile by the powder 
gases as they escape through the annular opening around its base 
before it has entirely cleared the muzzle. 

It has finally been determined, however, that a high velocity 
(2500 to 3000 f. s.) projectile will give slight increase in range 
without loss of accuracy if the rear end is coned between 5 0 and 8° 
for a distance of from approximately .25 to .75 calibers, the angle 
of the cone between those limits depending on the velocity and 
form of ogive. 



Base of 6-Inch CL. B. Pro- Base of 14-Inch CL. B. Projectile 

jectile, 3000 F. S. Gun. 3000 F. S. Gun. 

Fig. hi.—Boat-Tailing. 


In cartridge-case projectiles another factor is added in con¬ 
nection with the form of the after end, for in such projectiles that 
portion must be kept cylindrical for a considerable length in order 
to provide a proper bearing for the cartridge case. 

Form of Body. 

621 . Between the ends, whatever their shape and length, is the 
cylindrical portion or body of the projectile. At the after end of 
the body is the rotating band or bands, and at the forward end is 
the bourrelet. Between these two parts the diameter of the body 
is slightly reduced, in order to provide a generous clearance from 
the bore of the gun. It is the support and bearing provided by 
the band and bourrelet which steady the projectile in its travel 
through the gun and it is quite evident, therefore, that there must 















Projectiles 


499 


be a reasonable distance between them, else too heavy a duty 
will be demanded of them in preventing wobbling. There is no 
fixed rule as to what this distance must be, but designers generally 
allow about one caliber for minor-caliber projectiles and increase 
the distance gradually up to about 1.4 calibers in major-caliber 
projectiles. We have touched on the benefits of stream lining the 
forward and after ends, and also on the limitations on lengthening 
the projectile as a whole. Considering these points in connection 
with the distance between band and bourrelet, we can at once 
appreciate the reason why projectile design is a compromise, 
and why advantage cannot he taken to the utmost of promising 
individual features. 

Exterior Finish. 

622 . As a general rule projectiles are given, except on the 
bourrelet, only a rough machine finish, that is, one which, while 
smooth to the eye from a distance of say eight or ten feet, shows 
on closer inspection the marks of the turning tools. It is a popular 
fallacy that a smooth finish is conducive to accuracy. A very com¬ 
plete experimental firing was carried out some years ago in which 
a series of 14-inch target and armor-piercing projectiles were 
fired at a standard elevation, velocity and projectile weight; half 
of the projectiles being carefully ground and polished to a fine 
finish, while the other half were left with the usual finish. The 
difference in finish appeared to have negligible effect on the dis¬ 
persion; in fact those projectiles with the rough or service finish 
gave a smaller dispersion than did those with the polish! 

Weight. 

623 . Within reasonable limits projectiles can be given various 
weights for a given gun. The relation between weight of pro¬ 
jectile and powder charge, muzzle velocity and pressure is a part 
of interior ballistics. The weight of all U. S. Naval projectiles 
follows a definite system of apportionment, which, stated in 
calibers, is as follows: 



where 

w — approximate weight of projectile in pounds. 
d — caliber of gun in inches. 


500 


Naval Ordnance 


The weight of projectile per square inch of bore is called the 
sectional density of the projectile and is represented by the fol¬ 
lowing expression: 

S D — W 
u.- A , 

where 

S. D. = sectional density. 

W— weight of projectile in pounds. 

A = area of bore, including grooves, in sq. in. 

This figure has frequent application in gun and projectile de¬ 
sign. It will be recognized as one of the factors in the empirical 
formula in the paragraph on Rotation (paragraph 633). The 
sectional density varies from 0.635 f° r a 1-pounder up to 10.44 f° r 
a 16-inch, averaging approximately .6 of the caliber. 

The distribution of the weight in a projectile is a matter of con¬ 
siderable importance. As a general rule, the center of gravity 
should be in the longitudinal axis and close to or abaft the center 
of form. Slight variations in the location of the center of gravity, 
with respect to the center of form, have negligible effect on the 
dispersion. For instance, the center of gravity of an 8-inch pro¬ 
jectile was moved back and forth .5 inch, in a series of firings, 
without showing any appreciable effect on the dispersion. And 
similarly, the center of gravity of a series of 12-inch projectiles 
was moved to one side of the longitudinal axis, .013 inch, .039 inch, 
and .052 inch, respectively, without producing appreciable effect in 
the range or dispersion. 

The Bourrelet. 

624 . The “ bourrelet ” (see Plate I) is, as was stated previously, 
the forward bearing, so to speak, of the projectile. Its surface is 
generally ground to a fine finish in order to reduce friction and to 
prevent wear of the lands of the gun. This bearing surface is 
generally about one-sixth caliber in width, that is, longitudinally 
with the projectile. Some few small projectiles have no real 
bourrelet, the entire body of the projectile forward of the band 
replacing it. 

The bore of a gun becomes “ coppered ” after repeated firing, 
with a fine deposit of copper from the projectiles’ rotating band. 
And frequently, also, the liner in a gun becomes slightly crumpled 


Projectiles 


5 OT 

or ridged, after repeated firing, particularly in wake of internal 
shoulders. (See paragraph 341.) A certain clearance must, 
therefore, be provided between the bourrelet and the lands. The 
standard U. S. Navy practice is to make the bourrelet diameter 
.015 inches smaller than the bore of the gun. A minus manu¬ 
facturing tolerance is added to this diameter of another .015 inch, 
so that the average clearance is about .012 inches. Clearances of 
.05 inches have practically no effect on the dispersion, but it is 
reasonable to assume that unnecessary clearance can have at least 
no beneficial action, and may have an injurious effect on the lands, 
due to the blows of possible wobbling. It is quite apparent, also, 
that the less the clearance, the more accurate will be the initial 
direction of the trajectory. 

In a few instances a centering band of copper replaces the 
bourrelet, but as yet this system has not had wide application. 
It is generally conceded to be inapplicable to armor-piercing pro- 
jectiles, as the “ score ” would weaken the projectile at a vital 
locality. 

Rifling. 

625 . The rifling cut in the bore of a gun consists of spiral 
grooves whose function is to engrave the rotating band immedi¬ 
ately after the projectile begins its motion and then to cause rota¬ 
tion as the motion continues. For the engraving of the band the 
rifling is slightly coned at the origin, to fit the conical part of the 

band, and this is called the band slope. 

Most U. S. Naval guns now in service contain rifling in which 
the grooves occupy, at the muzzle, about half the circumference, 
or in other words, lands and grooves are of about equal width. 
This practice is by no means universal, and there are frequent 
instances where the grooves are as much as twice the width of the 
lands. It will be noted that the ratio between width of lands and 
grooves has been qualified by specifying at the muzzle. The 
reason is that grooves are generally tapered in width, being wider 
at the origin of rifling than at the muzzle. In other words, the 
land is wider at the muzzle than at the origin of rifling; this 
widening is called the “ increased forcing ” of the projectile. This 
is done to assist in maintaining the gas seal. It is easily appreci¬ 
ated that the maximum wear of band occurs against, the driving 
edge of the land. If the land widens as the projectile moves down 


502 


Naval Ordnance 


the bore, the increase in width may compensate for the wear. This 
question is intimately connected with the question of “ increasing ” 
and “ uniform ” twist, which is discussed later. It will be apparent 
that if the twist is variable, or increasing, the change of angularity 
of the land with respect to the band may have about the same 
effect on the gas seal as will the widening of the land. Many 
guns in service of 5-inch caliber and above, with both uniform and 
increasing twist, have lands of increasing width. This increase 
has gone as high as .40 inch in 1000 inches of length. At present 
it is the practice to maintain a constant ratio between width of land 
and groove in increasing twist guns, and to widen the land at the 
rate of .08 inch per 1000 inches in uniform twist guns. 

Where the bottoms of the grooves are concentric with the bore 
and their edges are approximately radial, the rifling is said to be 
" plain-section ” and is usually spoken of as “ ribbed ” rifling. But 
where the driving side of the groove is the arc of a circle of small 
radius and the trailing side is the arc of a circle of large radius, or 
a straight line at a large angle to the radius of the bore, the rifling 
is said to be " hook-section ” or simply “ hooked.’’ 

Sharp corners at the bottom of grooves are considered as in¬ 
jurious, the theory being that they facilitate the formation of heat 
cracks and accelerate erosion. Liberal fillets are, therefore, pro¬ 
vided at the bottom of grooves. Sharp corners at the corners of 
the lands are also eliminated but with fillets of smaller radius. 

Hooked rifling has been extensively used in the U. S. Navy 
and guns of various types and calibers up to 14-inch will be found 
in service. In recent years, however, no guns of 14-inch or above 
have been designed with hooked rifling. 

626 . The depth of the groove depends on several factors; the 
muzzle velocity, pressure, width of band, type of rifling, sectional 
density of projectile, and caliber of the gun, all requiring due con¬ 
sideration. In a gun designed for high pressures, or high rota¬ 
tion of projectile, the driving area must be large and this can only 
be secured by deepening the groove or widening the band. Very 
deep grooves are injurious as such a form is considered to be 
conducive to the formation of heat cracks and the acceleration 
of erosion. No simple rule can be given, therefore, to govern the 
depth of grooves, although, speaking generally, the depth will lie 
between ^ and 1 per cent of the caliber. 


Projectiles 


31* 50 CALIBRE 
PROFILE AT MUZZLE 
MODERN RIB RIFLING 



5!“ 40 CALIBRE 
PROFILE AT MUZZLE 
OLD STYLE RIB RIFLING 



550 CALIBRE 
PROFILE AT MUZZLE 
HOOK RIFLING 



6^ 53 CALIBRE 
PROFILE AT MUZZLE 
MODERN RIB RIFLING 



1-4-— 50 CALIBRE 
PROFILE AT MUZZLE 
MODERN RIB RIFLING 



Fig. iiia. 











504 


Naval Ordnance 


627 . As is the case with the depth of grooves, no fixed rule can 
be given for their number. The number of grooves is generally 
expressed as a function of the caliber in inches, thus 7.5 grooves 
per caliber would give 30 grooves for a 4-inch gun. There are 
certain guns of almost every caliber in the U. S. Navy where the 
grooves number six times the caliber and that number not only 
expresses the average past practice, but is also the present practice. 
In small guns the factor is increased and has gone as high as 10. 
Many old guns in our service from 5-inch to 13-inch, inclusive, 
were, however, as low as four grooves per inch of caliber. Some 
of the most successful ordnance engineers in Europe are now using 
about 7.5 grooves per inch of caliber. 

628 . The amount of “ twist ” is generally expressed in America 
by the number of calibers traveled during one revolution of the 
projectile, as for instance, one turn in 25 calibers. In continental 
Europe, the twist is frequently expressed by the angle between the 
groove and a plane passing through the axis of the bore. The 
relation between these two quantities may be expressed as follows: 

tan 0 = —^-where 6 = angle of twist. 

calibers for 1 turn 

As the tangent of small angles is approximately equal to the 
angle in radians, this relation can be approximated by the thumb 
rule of dividing 180 by the number of calibers required for one 
turn to secure the angularity. Thus a twist of 1 in 25 is approxi¬ 
mately 7 0 . The twist of rifling is also frequently called “ pitch.’' 

629 . The rotation of a projectile is seldom expressed in 
R. P. M., but it is interesting to calculate it in order to compare 
it with that of other rotating machinery, as follows: 

r p jyj __ (Muzzle v elocity in f. s.) x 720 

(Twist in cal. per rev.) Xcaliber in inches 

Thus, a 6-inch gun, at 2800 f. s., rifled 1 in 30. gives its pro¬ 
jectile 11,200 R. P. M. 

630 . Twist can be either uniform or increasing. In “uniform 
Hoist ” the grooves follow a uniform spiral, or, in other words, are 
inclined at a constant angle to the axis of the bore. In “ increasing 
twist ” the grooves possess little or no twist at the origin, but 
gradually increase the twist toward the muzzle. When the rifling 
begins with O twist and uniformly increases the developed curve 





Projectiles 


505 


is a parabola, and such a twist is generally called “ parabolic 
twist.” Increasing twist may be a combination of various uniform 
twists, connected by parabolic or easy curves. All increasing 
twists in U. S. naval guns are semi-cubic parabolas. Fig. 107 shows 
the developed curves of three forms of rifling— A, being uniform 
twist: B, a parabolic twist; and C, a combination, 1 to 50 to 1 in 32 
twist, the final twist in all three being the same. 

631 . When rifling was first applied to cannon design, it was 
without exception made uniform. At that time slow-burning 
powders as we now know them were unknown, and in unifoim 



pitch the instant at which maximum torque is applied to the pro¬ 
jectile coincides with the instant of maximum chamber pressure. 
These two factors imposed a very sudden and large torque early in 
the travel. It is quite evident, therefore, that under these con, 
ditions, a reduction in the initial twist effected a reduction in the 
maximum torque. Also, a delay in the instant of maximum torque 
results in a slight slowing down of the powder. These influences 
lead to the introduction and development of increasing twist, and 
combinations of increasing and uniform twist. 

Most of the guns now in service have increasing twist, the rifling 
beginning with zero twist and ending with 1 in 25 twist, although 
the larger guns now in service begin with a twist between 1 in 40 

and 1 in 50. 






























































































































































5°6 


Naval Ordnance 


632 . Progress in gun and ammunition design is, however, 
gradually diminishing, if it has not already eliminated, the ad¬ 
vantages of increasing twist over uniform twist. Guns are longer, 
pressures higher, power greater, and muzzle velocity higher; 
while powder is being made to burn slower and increase the muzzle 
pressure. As applied to a modern high-powered gun, the relative 
merits of the two systems may be summarized as follows: 


Increasing Twist. 

1. Reduces the maximum torque on the projectile. 

2. Is considered to reduce erosion, by reducing the work on the 
lands where the erosion is greatest, that is, near the origin of 
rifling. 

3. Necessitates as narrow a band as possible, and consequently 
one band. 

4. Results in considerable shearing of the band, especially in 
long bigh-powered guns, with wide bands on the projectile. 

5. Probably causes additional copper deposit in the middle third 
of the bore. 

Uniform Pitch. 


1. Permits a band of any width or as many bands as desired. 

2. Reduces the torsional strain on the muzzle of the gun. 

3. Consumes less energy in moving the projectile through the 
bore, and hence delivers a greater muzzle energy. 

4. Gives a clean-cut engraving to the rotating band. 

633 . The riflings of most American, and many European can¬ 
non, were tabulated by Mr. C. F. Jeansen, of the Bureau of 
Ordnance, who deduced therefrom the following empirical 
formula: 


Where 


7=4- X 
a 


— x 1 

A K' 


T — twist in calibers at muzzle. 
v — muzzle velocity in f. s. 
d — diameter of bore in feet. 
w = weight of projectile in pounds. 

A — area of bore in sq. in. (including grooves). 
K — factor of reduction. 


Tbe application of this formula to the tabulation of guns gives 
an average value for K of 640. Such guns as have shown the 



Projectiles 


50/ 


most satisfactory accuracy and life give a value very close to this 
figure, and it has been suggested therefore that the value of 
(640=51150) be given for future design. 

This formula, while useful, is not capable of mathematical 
demonstration. Applying it to a 6-inch 2800 f. s. gun, with 105- 
pound projectile, we would get a final twist of about 1 in 33.5 
calibers. 

The Rotating Band.* 

634 . The rotating band has three specific functions—to seal 
the bore, to steady and center the rear end of the projectile, and to 
rotate the projectile. It is also utilized to prevent over-ramming 
in worn guns and to hold the projectile in place during loading and 
elevating for firing. In addition to these functions the band has 
considerable effect on the range, dispersion, muzzle velocity and 
life of the gun. 




BAND SCORE WAVE BAND SCORE KNURL SAND SCORE NOTCH 

Fig. i 13.—Methods of Preventing Supping of Rotating Band. 

Rotating bands are made of commercially pure copper for all 
minor and medium caliber projectiles, and of cupro-nickel alloy 
containing 2.5 per cent nickel for major-caliber projectiles, the 
nickel being added to secure greater strength. 

As a general rule rotating bands are about ^ caliber in width. In 
some instances, particularly abroad, the width of a band is kept 
down to a maximum of about 1.5 to 2.0 inches, and where a greater 
strength is necessary two separate bands, separated by a short 
distance, are provided. This system has considerable merit. 

The band is secured in a score cut in the projectile body, there 
being a dovetail on each edge to assist in overcoming centrifugal 
force, and either waved ridges, longitudinal nicks, or knurling in 
the bottom of the score to insure against slipping during accelera¬ 
tion. The band is made as a ring of slightly greater internal 

* Rotating Bands are also called “ Forcing Bands.” 











































































5°8 


Naval Ordnance 


diameter than that of the body and is slipped over the score, while 
hot, and pressed radially into place in a powerful hydraulic press 
called a “ banding press.” (Fig. 114.) 

635 . The forward edge of the band is slightly conical and fits 
into a correspondingly coned seat at the origin of rifling. 

The central portion of the band is generally cylindrical and of 
a slightly greater diameter than the diameter of the bore including 
grooves. An expression, often used to obtain the diameter is 
D = C + 2p +.02 where C is the caliber of the gun, and p the depth 
of the grooves. 



Fir,. T14 .—Banding Prf.ss. 


It will be observed (Fig. 115) that on the rear part of practically 
all bands is a raised lip. This lip serves the purpose of insuring a 
good gas check and at the same time, because of its considerably 
greater diameter, preventing over-ramming in a worn or eroded 
gun. 

When the gun is fired and the pressure rises, the projectile is 
forced into the rifling which then engraves the band to fit the 
contour of the bore, and the revolution of the projectile ensues. 
It is easily seen that the driving face of the lands should be radial 
so that the rotative force will be applied normally. 

636 . With uniform twist rifling the lands in the bore present a 
constant angle to the band. After the first engraving, therefore, 





Projectiles 


509 


there is no further flow to the metal in the bands other than the 
slight drag and wear due to friction. With parabolic or increas¬ 
ing twist rifling, however, the lands in the bore present a con¬ 
stantly increasing angle to the band. In this case, therefore, 



IA INCH CLASS B 



6 INCH COMMON 



A INCH COMMON 



12 INCH (SPECIAL) BRITISH 


Fig. 115. 


A B 6 



F 0 E C H 

Fig. 116. 


there is a continual flow of metal due to the changing pitch of the 
thread. This condition is shown in Fig. 116, which diagrammat- 
ically represents the parts of an engraved band covering three 

grooves in the rifling. 























Naval Ordnance 


5 1Q 

The shaded portions represent the imprint of the land on the 
band when the projectile leaves the muzzle, A D being the initial 
driving edge with the smaller twist and A F being the final driving 
edge with the larger twist. During the travel of the projectile 
down the bore the imprint of the land has been shifted from A B 
C D to A B E F. It is evident, therefore, that the copper under 
A D F has been removed during the travel and that the projection 
on the band which remains in the groove of the gun is covered by 
B G H C. This loss of copper is exhibited by increased friction 
in the bore, some authorities stating that increasing tw’ist creates 
2 t, times as much frictional loss of energy as does uniform twist. 

637 . In order to insure a tight joint, especially in eroded guns, 
the diameter of the cylindrical portion of the band is generally 
a few thousandths of an inch greater than the diameter of the bore 
across grooves. It is clearly evident, however, that any excess 
metal in the band will be pressed or wiped back toward the base 
of the projectile, this being more pronounced in wake of the lands. 
Should this excess metal be of sufficient quantity it will form a 
scalloped skirt extending abaft the band score. Now at the 
instant that this skirt clears the muzzle there will be a rush of gas 
past it, which, aided possibly by centrifugal force, may turn this 
skirt out radially at a considerable angle. This is called fringing 
and a pronounced fringe can have a material effect on the range 
and dispersion, the effect being greatest on minor and medium 
caliber projectiles. 

The successful design must not only provide sufficient metal 
in the band to secure the desired performance, but must also 
insure against fringing. Grooves or “ cannelures ” are placed in 
the middle portion of large bands, for the purpose of allowing 
space for this excess copper and a large groove is also frequently 
provided abaft the lip to take this excess copper. 

638 . It is important to fix upon the position of the forcing band 
(rotating band) and the precise distance from the rear edge of the 
band to the base of the projectile, and is even more important, when 
the caliber is smaller, than the forcing and indentation of the 
grooves. The resultant of pressure on the base of the projectile is 
seldom axial with the bore; it is usually inclined to this axis, and 
does not pass through the center of the base. This eccentric and 
oblique action of the resultant gives rise to a couple, which tends to 


Projectiles 


5i 1 

rotate the projectile about one of the diameters of the forcing-band, 
and to produce jolting or beating along the walls of the gun (“ ba- 
lottement”); the projectile leaves the piece with perturbations, 
which do not allow an efficient overcoming of the air resistance, and 
which produce a sensible diminution of range and accuracy of 
fire. Experiments have shown that there is one particular posi¬ 
tion of the band in which this couple, to which the projectile owes 
its perturbations, is reduced to a minimum, and to which, as a part 
of other conditions, the maximum range and best stability of flight 
correspond. In this position the rear edge of band is one inch 
from the base of the projectile. 

Stability and Flight. 

639 . The mathematical demonstration of the stability of pro¬ 
jectiles is not only without the scope of this work, but is by no 
means in a settled condition. The difficulty lies in our inability to 
determine the precise nature of the forces acting on the projectile 
in flight. 

The gyroscopic effect of the rotation of the projectile is to 
stabilize or hold its axis in a fixed position in space. Were this 
action to remain unaffected by external force, the projectile would 
travel with its axis always at the same angle with the horizontal, 
and would strike with its axis at an angle to its direction of travel 
equal to the sum of the angles of departure and fall. Experiments 
have shown, however, that the axis of a projectile, having a 
smooth flight, is practically in the trajectory at the point of fall, 
and presumably therefore throughout its entire flight. The effect 
of atmospheric resistance is, therefore, not only to slow down its 
rotation and translation, but to form with the gyroscopic force, 
a “ couple ” which effects a continual tipping down of the forward 
end of its longitudinal axis. It is quite evident, therefore, that 
there must be a specific rotational speed most suited, for a given 
projectile, to a particular velocity. 

The balance of this couple is an important feature in any discus¬ 
sion of rotation. If the resultant of the couple created by the 
atmospheric resistance preponderates, the projectile ceases to be 
stable, and tumbles. If the gyroscopic force preponderates the 
projectile refuses to tip and a complex series of forces immediately 
ensues which causes the projectile to corkscrew. The balance is 


512 


Naval Ordnance 


not restricted to a precise relation, but allows certain limits between 
which the flight is smooth and stable. 

640 . A study of the plotted trajectory of any projectile will 
show that its curvature is small during the early stages and final 
stages hut is large during the middle stage, the maximum curva¬ 
ture being in the immediate vicinity of the vertex. That is to say, 
therefore, that the yielding or tipping of the axis must accomplish 
a much greater and more rapid change in direction while in the 
neighborhood of the vertex than in any other position of the 
trajectory. 

It is generally accepted that the atmosphere has a greater retard¬ 
ing effect on the translational velocity, than on the rotational 
velocity. This being true, the ratio between translational energy 
and rotational energy continually decreases during flight; or in 
other words, the gyroscopic force continually increases in rela¬ 
tive proportion, or again, a projectile which starts with a mini¬ 
mum margin of rotation gradually increases that margin. 

If might be mentioned parenthetically that experiments have 
been recently undertaken, principally abroad, to put vanes on the 
ogive which will increase the rotational retardation and tend, 
therefore, to preserve the initial ratio between the rotational and 
translational velocities. 

Now, from the above it is evident that the performance of the 
projectile at the vertex is the essential feature of a study of its 
rotation. It should be noted that with low angles of elevation, or 
flat trajectories, the curvature at the vertex is so slight as to 
require no special consideration, but as the elevation increases the 
curvature becomes greater until at angles of elevation of about 
6 o° or greater the curvature at the vertex is abrupt, and at such 
angles a projectile will not dip sufficiently, but may either tumble 
or descend base first. We may now consider the phenomena which 
enable us to fix the proper rotation to give a certain projectile. 

641 . If a projectile is launched with insufficient rotation, the 
gyroscopic force is overcome by the resultant of the external 
forces and the projectile “ tumbles ” or goes end over end. This 
is discernible through pronounced and intermittent sound devel¬ 
oped during early flight and excessive dispersion. It is also deter¬ 
mined by firing the projectile through cardboard screens. In 
service such phenomena are exhibited in old guns with such badly 


Projectiles 


513 


eroded bores that the rifling is unable to impart the designed rota¬ 
tion to the projectile. Projectiles with insufficient rotation have 
been known to turn sideways within 100 feet of the gun. 

If a projectile is launched with excessive rotation, there is little 
early indication of difficulty, other than excessive drift, and little 
effect on short ranges with flat trajectories. As the elevation is 
increased, however, and vertices are reached which require rapid 
change in inclination or dipping, the gyroscopic forces prepon¬ 
derate, a corkscrew path results, and the visible effect is excessive 
dispersion. 

In other words, insufficient rotation is connected with short 
range phenomena, while excessive rotation is, speaking broadly, 
connected with long range phenomena. 

Under-Water Attack. 

642 . When an ogival-headed projectile, traveling in air, strikes 
water, it deviates from its trajectory in a violent and uncertain 
manner. At small angles of fall it tips up, runs parallel with the 
surface for a short distance and then, if it still has sufficient 
velocity, emerges and again takes to the air. This is called a 
ricochet. At greater angles of fall it is liable to deviate in any 
irregular direction. 

The desirability of the attack of submarines by gun fire from 
surface or aircraft has resulted in the development of projectiles 
which maintain their trajectory, upon entering water, with reason¬ 
able accuracy. In these projectiles the ogival form is abandoned 
and a square head is substituted. Such projectiles are called, in 
our navy, “ Plat Nose projectdes and elsewhere are lefetred to 
as “ diving shell.” (Plate I, Figs. 1 and 2.) 

The retardation of the translational velocity of these projectiles 
in both air and water is excessive, but such a sacrifice has to be 
made in order to secure accuracy upon and after water impact. 
Interesting proposals have been made to fit flat-nose projectdes 
with thin wind shields or false ogives which will collapse and be 
wrenched adrift upon impact with water, thereby preserving both 
good flight in the air and under-water accuracy. 

Classification. 

643 . The impact damage which a projectile itself does is 
entirely secondary to that which results from its burst. The design 


34 


514 


Naval Ordnance 


of most projectiles is based primarily on using the projectile as a 
vehicle with which to carry a quantity of explosive into a ship and 
secondarily to provide missiles with which to carry the force of the 
explosion. 

Where the projectile must meet heavy face-hardened armor the 
result is a massive piece of steel with a heavy head, thick walls and 
a small cavity, called an armor-piercing projectile. In such 
projectiles the weight of the bursting charge (high explosive) 
varies between 2.1 per cent to 2.6 per cent of the total weight of the 
projectile. If the size of the charge is increased the projectile is 
unequal to matching even caliber plate at battle ranges and angles 
of fall, while if the size of the charge is reduced the fragmenta¬ 
tion of the projectile on burst is not efficient. (Plate I, Fig. 3.) 

Where the projectile may encounter only a combination of light 
side plating, bulkheads, and decks, the cavity can be somewhat 
enlarged, and the design is called a common projectile. In such 
projectiles the charge represents, for medium and major calibers, 
about 6.0 per cent of the total weight, and for sizes below 6-inch 
the percentage falls to about 3.0 per cent to 3.5 per cent. (Plate I, 
Fig- 4-) 

And finally, where the steel envelope is made only sufficiently 
strong to stand the shock of firing or “ set-back ” (see Art. 691), 
in the gun, the cavity is as large as possible, the design is called, 
in the American Navy, a Class B projectile, and by ordnance 
engineers in general a high-capacity projectile. (Plate I, Figs. 1, 
2, 5 and 6). Such projectiles are fitted to burst on impact. It 
should be noted that the strength of the walls of such projectiles 
is fixed by the set-back; in consequence the lower the muzzle 
velocity of the gun, the greater will be the relative size of the 
cavity, for a given weight of projectile. In high-velocity (3000 
f. s.) ogival-headed projectiles, the weight of charge can be carried 
as high as 10 per cent to 12 per cent of the total projectile weight, 
and in low-velocity (1000 f. s.) flat-nose projectiles, the weight 
of charge can be increased as high as about 25 per cent of the total 
projectile weight. 

There is another class which finds favor in certain countries, 
called semi-armor-piercers. These projectiles are between the 
armor piercer and the common, and are designed to match a half¬ 
caliber plate at battle ranges and angles of fall. They carry about 
3.5 per cent to 4.0 per cent of their weight in the bursting charge. 


CHAPTER XV. 


PLATE I. 



S IN. CL. B PROJECTILE 
flat nosed 

WEIGHT OF CHARGE _ _- „ v 
WEIGHT OF PROJECTILE - ^ 4 

Fig. i. 



12 IM A -P PeOJECTILE 

weight of charge _ _ £ 
WEIGHT OF PROJECTILE 

Fig. 3 . 



3 IN. HIGH CAPACITY SHELL 

Fig. 5 . 


BURSTING CHAESE 




///////////////////////////S7W7 


FUZE HOLE 


BOURRELET 


3 PDR PROJECTILE 
CUP-NOSED 



OGIVE 

CENTER. 


5 1 


fe IN. PROJECTILE (COMMON) 

WEIGHT OF CHARGE - ft 00, „/ 
WEIGHT OF PROJECTILE ~ * > ' OS 

Fig. 4 . 

EXAMPLES OF PROJECTILES. 


WEIGHT OF CHARGE _ 
WEIGHT OF PROJECTILE ~ 5 1° 

Fig. 6 . 



NT 


IA IN. CL. B PgQJECTILE 


Fig. 2 . 








































































































































































































































Projectiles 


5LS 


In addition to the three above mentioned general classes, are 
other special projectiles such as shrapnel, illuminating projectiles 
or star shell, smoke and gas shell. 

Let us now examine these projectiles in detail. 

The Armor-Piercing Projectile. 

644 . The predominating school of thought during the Civil 
War, in connection with the attack of armor, was to smash in the 
armored side of a vessel with solid shot and spread splinters from 
the broken projectile, plate and backing, over the back areas; 
rather than to penetrate the armor and burst the projectile in the 
rear. As noted in Art. 593, this theory had a short life and the 
introduction of rifling finished it. It was a long time, however, 
before the use of the solid shot was abandoned. As late as about 
1895 solid shot were made for armor penetration only. There 
are, however, frequent revivals of variations of the “ smashing 
effect.” The development of high explosives led to the advance¬ 
ment of the theory that a large quantity exploded against the 
armored side of a vessel would cave in the armor and plating and 
completely destroy that part of the vessel in the general neighbor¬ 
hood of the impact. Costly and elaborate experiments, carried 
out in this country during the past 10 years, have conclusively 
shown that high-capacity, high-explosive projectiles detonating on 
the armored side of a vessel have no appreciable effect on the 
armor and negligible effect on the adjacent ship’s structure. 
Furthermore, the engagements of the World War show beyond 
doubt that, while major-caliber Class B or common projectiles 
may produce great havoc in upper works and unarmored locali¬ 
ties, modern armored vessels are almost immune to disablement by 
other than armor-piercing projectiles of the finest quality. 

The first development in armor piercers, after the ordinary cast- 
iron shot, was the Palliser chilled-iron projectile, which was intro¬ 
duced in England in 1866. This projectile was an iron casting, 
cast point down, the lower part of the mold being an iron chill 
while the upper part was sand. These and similar projectiles were 
used up until about the introduction of steel armor. It is quite 
probable that cheapness was an important factor in their con¬ 
tinued use, for in 1862 Whitworth patented a case-hardened heat- 
treated mild-steel projectile with a hard head and soft base. 


Naval Ordnance 


5i6 

Wrought iron was frequently tried, but due to its inherent 
ductility never made any headway. In 1878 extensive trials at 
Shoeburyness showed that the Whitworth projectile had surpassed 
all other makes in penetrative qualities. 

But about this time the firm of Jacob Holtzer et Cie. in France 
produced a forged high-carbon, nickel-chrome, crucible steel 
armor piercer which, in spite of the efforts of rival manufacturers 
to duplicate, remained the most efficient projectile in existence for 
many years. In 1886 the Navy Department secured a few Holtzer 
projectiles from St. diamond. These contained about 1.80 per 
cent chrome and .80 per cent carbon. Shortly after this the 
Holtzer and rival processes were imported into America. 

645 . The next real development in armor piercers was the 
introduction of the cap. In 1878 a comparative test was made in 
Europe of the effects of projectiles against the face and back of a 
compound plate. The same projectile which smashed on the 
face completely penetrated when the plate was reversed. A thin 
wrought-iron plate was then placed in front of the hard face and 
this was found to materially increase penetration. And finally a 
wrought-iron jacket was placed over the point of the shot which 
gave the same result of increased penetration. It appears to be 
authentically established that in 1883 Colonel Inglis of the English 
Ordnance Committee devised the first soft-steel caps. In 1896 
Mr. I. G. Johnson submitted some 6-inch solid fluid-compressed 
steel shot to the Navy Department on the noses of which he had 
placed a small cylindrical mild-steel cap. An important feature 
of these caps was that an annular space was left between the point 
of the projectile and the rear portion of the interior surface of the 
cap, which was filled with graphite. These projectiles completely 
penetrated a 7-inch Harvey plate when striking at 2100 f. s., while 
similar uncapped projectiles at the same striking velocity smashed 
on the plate. Shortly after this, caps were placed on all American 
armor piercers, but the graphite feature was later abandoned. 
A few years ago the cap was improved by making it of high- 
carbon chrome steel and hardening it decrementally, although the 
idea had been patented in 1896. 

Since the introduction of forged high-carbon nickel-chrome 
steel and the cap, there have been no radical improvements in 
armor-piercing projectile manufacture, other than a gradual in- 





Projectiles 


517 


crease in skill of manufacture. Up until comparatively few years 
ago armor piercers were always made from crucible steel, but in 
the late nineties the use of small open hearths began and now most 
armor piercers are made from open-hearth and electric steel. 

Manufacture of Armor-Piercing Projectiles. 

646 . Open-hearth steels—acid, basic, and electric—are used for 
these projectiles, but the melting is given far greater care than is 
received by the average commercial steel. 

The ingots are cast nose down in iron moulds in order to chill 
them rapidly to prevent piping and injurious segregation. 

There are two general systems of forging. In one the ingot is 
cast of greater diameter than the finished projectile, and is forged 
down, being lengthened in the process, under a press or hammer, 
and in this process the cavity is bored out. In the other process, 
the ingot is of smaller diameter than the finished projectile, is 
upset in a die under a press to the proper diameter, and its base 
is then pierced by a punch to form the cavity, the rear walls of the 
body being somewhat extruded. In the first process mentioned 
the grain or fiber of the steel is longitudinal whereas in the other 
process it is transverse. 

The rough forgings are then annealed, after which they are 
rough machined nearly to size. The next step is a series of heat¬ 
ings and quenchings in oil and hot water for the purpose of 
refining and fibering the grain structure. After this treatment the 
forging is turned to exterior and interior dimensions, allowance 
being made for the fitting of base plug, and finishing of band score 
and bourrelet. 

The next step is the hardening, which is accomplished by a 
graduated heating beginning with the point followed by a com¬ 
plete quench in agitated cold water. This puts the entire pro¬ 
jectile in an exceedingly hard condition. The heating for this 
treatment is generally accomplished in a bath of molten lead, such 
procedure being conducive to accurate control of both temperature 
and position of application of heat. After this the base of the 
projectile is heated to a lower temperature than was used for 
quenching and upon withdrawal from the bath or furnace is sus¬ 
pended nose down and immersed up to the bourrelet in agitated 
cold water. This procedure draws or tempers the rear portion 


Naval Ordnance 


5i8 

while preserving the hardness in the head. The result is an ex¬ 
ceedingly hard head to the rear of which the hardness gradually 
decreases with increase in toughness. The hard head is to effect 
the smashing of the plate's face while the tough rear is to support 
the head and stand the breaking strain of angle impact. (See 
Plate II.) 

Finally, the projectile is sand blasted, the band score is finished 
and the band pressed into place, the cap and wind shield is put on, 
the bourrelet is ground, the band is turned to size and the base 
plug fitted. 

647 . The cap follows, in general, the same methods of manu¬ 
facture and treatment as are applied to the projectile, although, of 
course, no special ingot is made for it. After forging it is annealed 
and rough turned, is then fibered, then finish machined, except 
threading for the wind shield, then decrementally hardened and 
finally finish turned and threaded and installed. Caps are made of 
the same kind of steel as are the projectile bodies, except that the 
carbon, nickel and chromium are not so high. 

Caps are secured to the projectile by several methods. The 
one most commonly used consists in peening the skirt of the cap 
into notches cut in the ogive of the projectile. Fig. 114, showing 
an armor piercer in the banding press, also show's the notches in 
the ogive. Another method consists in soldering the cap to the 
ogive with a special low melting point solder. Such a solder is 
required to prevent the heat necessary for soldering from drawing 
the temper of the ogive. 

Caps should be held securely in place, and it is quite probable 
that their efficiency on oblique impact is materially affected by the 
security of the bond. The notches in the ogive are certainly no 
source of strength. The use of solder is therefore looked upon 
with favor by many ordnance engineers. 

It occasionally happens that caps become loosened by rough 
handling. Such projectiles should be returned to an ammunition 
depot for recapping. 

648 . The wind shield is made of either cast iron or forged 
mild steel and has no special strength other than that necessary to 
prevent destruction during handling and set-back. Wind shields 
are generally screwed on the cap, and frequently the thread is cut 
on a tapered surface. After screwing home they are “ set ” by a 


CHAPTER XV. PLATE II 









r 


' 






520 


Naval Ordnance 


center punch at the joint. They sometimes become loose in hand¬ 
ling and in that event they should be tightened and reset. 

649 . Base plugs are simply ordinary good quality nickel-steel. 
The only special requirement is that their longitudinal axis should 
be normal to the longitudinal axis of the original ingot, a precau¬ 
tion taken to insure the maximum stregnth against shear or col¬ 
lapse under the chamber pressure of the gun, and to prevent piping 
or porosity from leading flame or gases in to the bursting charge. 
This latter precaution is taken with all projectile base plugs and 
will not be referred to again under other projectiles. 

650 . The steel for A. P. projectiles is the finest quality, nickel- 
chrome steel. Due to the comparatively small mass and more 
convenient size the carbon can be carried much higher than is 
possible in armor manufacture. For instance, we find the carbon 
content as high as .75 per cent. Similarly the chromium can be 
carried a little higher and we find the chromium content as high 
as 2.60 per cent. The nickel runs about the same as for armor. 

Penetration. 

651 . Calculations as to penetration are all based on the DeMarre 
formula, which was discussed under Armor, although with less 
reliability than in the case of armor. A projectile may penetrate 
or “ defeat ” a plate but break up in the process, which will, of 
course, prevent it from being burst. In considering penetration 
from the projectile standpoint, the standard of performance must 
be effective bursting condition after penetration. Effective burst¬ 
ing condition is generally taken as complete integrity of the cavity. 
Thus the projectile may loose its'nose, or even a large portion of 
the head down to about the bourrelet, but it is considered to be 
effective if the cavity is not exposed by cracks or fractures. 
(Plate II.) 

When a projectile strikes a plate normally and penetrates, with¬ 
out deformation, just so far that its bourrelet lias passed through 
the plate and beyond all ragged edges, it lias delivered to the plate 
all its energy, except for the heat generated in the projectile, which 
is comparatively slight. Now, it is generally accepted that such a 
condition represents the maximum delivery of energy which a 
projectile can accomplish. At higher velocities it is probable that 
the plate requires less energy to accomplish its defeat. No demon- 


Projectiles 


52i 

stration of the accuracy of this theory can be made as no satis¬ 
factory device has been developed with which to measure residual 
velocities, but it is founded on considerable observation. Such a 
theory being correct, it follows that, for normal impact, the higher 
the striking velocity the less the strain on the projectile. 

Now, as the angle of obliquity is increased from normal very 
different conditions are imposed. The primary phenomenon is 
that the projectile generally tends to readjust its axis toward the 
normal, or in other words, strives to seek normal penetration. 
This action, of course, introduces violent side strains, and when 
projectiles break on angle impact they clearly show this side strain 
by breaking across the body. The fact that rotation still persists 
must be remembered. Now it is clearly evident that in oblique 
impacts, the greater the velocity the greater must be the side or 
twisting strain. 

To reduce the combination of the two conditions mentioned 
above to mathematical terms has so far proved impossible. In 
comparing projectiles, therefore, their relative efficiency can only 
be determined by confining the comparison to certain arbitrarily 
fixed conditions. For instance, we may fix a specific angle of 
obliquity and vary the velocity to effect comparison or we may 
fix the velocity and vary the angle of obliquity to effect com¬ 
parison. Or, on the other hand we can fix the velocity and 
obliquity and vary the plate thickness required to defeat the 
projectile. 

The Action of the Cap. 

652 . Various theories have been advanced as to the reason for 
the increase in penetration secured by the application of the cap. 
The simplest, and perhaps the most reasonable, is that the cap 
acts to break down the initial strength of the plate, allowing the 
nose to reach an already strained surface and then provides power¬ 
ful circumferential support to the point and nose as they begin to 
penetrate the hard face, maintaining the support until they are 
well into the plate. This theory is supported by the fact that an 
un-capped projectile will penetrate a non-face-hardened plate with 
the same velocity as will a capped projectile, in fact with somewhat 
less velocity, as experiment has shown; the slight decrease being 
ascribed to the adding of the thickness of the cap to that of the 
plate. In comparing capped and un-capped projectiles against 


522 


Naval Ordnance 


face-hardened plate, recent experiments with 8-inch projectiles 
have shown that equal penetration can be secured when the 
energies are as about 5 to 9. 

And finally the cap has the efifect of increasing the biting angle; 
that is to say, a capped projectile will “ bite ” or fail to glance ofif 
at greater angles of obliquity than will the same projectile without 
a cap. This is due to the greater bluntness of the front end of the 
cap. 

Form of Internal Ogive. 

653 . The shape of the ogive of the projectile itself has con¬ 
siderable efifect on the efficiency of the projectile. The curvature 
of the ogive was increased to about 2.5 calibers because of tbe 
desire to reduce air resistance and this curvature was retained 
under the cap after its adoption. Shorter curvature is desirable, 
however, to secure a shorter projectile, and the modern tendency is 
to fix the ogive radius between 1.5 and 2.0 calibers. 

Common and Class B Projectiles. 

654 . The development of the common and Class B projectile 
followed logical channels, being based on the attack of unarmored 
vessels, the upper works of armored vessels, earthworks and forti¬ 
fications. 

As a general rule the design and selection of materials of these 
projectiles is predicated, in so far as is consistent with efficient 
operation, on cheapness and quantity production. I11 fact, the 
co-ordination between design and quantity production is of almost 
vital importance. These considerations led to the selection of 
plain .45 per cent to .60 per cent carbon basic open-hearth steel, 
and the adoption of a design which reduces the number of forging 
and machining operations to a minimum. In designs requiring the 
maximum attainable weight of bursting charge, or calling for 
peculiar interior arrangements, greater strength per unit of area 
will probably be required, in which case a higher carbon or even 
a nickel-steel may be necessary. 

Methods of fabrication differ with the caliber and type. In 
large calibers each projectile is made from a separate ingot, while 
in medium calibers large ingots are “ cogged down ” in a rolling 
mill to billets of round, square, or polygonal section and then cut 


Projectiles 


523 


or broken to proper length. I lie ends of these blanks are usuall} 
inspected to eliminate those which contain piping or injurious 
segregation. 

655 . Considering major and medium caliber projectiles, and the 
ingots or billets made for them, as mentioned above, fabi ication 
continues, in general, as follows (big. 117) : 

The projectile blank is heated, placed in a die approximating the 
exterior contour, nose down, but of excess diameter, and then 
pressed under the plunger of a hydraulic press, thus forming the 
ogive. A piercing die or plunger of slightly less diameter than 
the cavity is then forced into it, which forms the cavity. These 
two steps can be done with one heating. 



Fig. 117- 


In some projectiles this is the only forging required, but gen¬ 
erally the extrusion performed by the piercing die is insufficient 
to make the cavity long enough. In this case, which is quite gen¬ 
eral. the forging or blank is reheated, and placed in a draw-bench, 
the nose being placed in a die containing a circular hole slightly 
larger than the finished diameter, and it is then forced through this 
drawing die by a hydraulically operated plunger which is inserted 
in the "already partially formed cavity. This drawing process 
forces the sides back over the plunger, thus extending the blank 
to the required length. In some cases more than one draw is 
required, and this is generally performed in one heat by forcing 
the forging through several rings or dies in succession in the same 
draw-bench. The method just described applies, of course, to open- 











































524 


Naval Ordnance 


base projectiles. Where the base is to he solid and the nose is to 
be open the same general process is followed, except that the 
projectile is worked from the base instead of from the nose. 

The blank is then generally annealed, or normalized, and if high 
physical properties are required, it may be heat-treated to secure 
them. It is then passed to the machine shop for finishing. 

The finishing consists in turning and boring to the correct 
dimensions and tolerances, banding, fitting the plug, painting the 
interior of the cavity and inspecting and stamping for shipment. 
As a general rule all surfaces are finish machined except as noted 
below. Many efforts have been made to omit the machining of 
the cavity but the forge finish is not satisfactory because the 
forging temperature is so high that a rough and scaly surface 
results. 

Some projectiles are fitted with heavy nose or base plugs, others 
have smaller adapters to carry the fuse, and others may be designed 
to receive the fuse itself. In most of these classes the cavity is 
always of larger diameter than is the hole for these fittings. This 
condition is met in two ways. 

Where the hole is large and the amount of metal to be removed 
from the rough forged cavity is small, or where the projectile is 
completely heat-treated, the interior is finished in a boring machine 
or lathe, using a tool on the end of a bar which is inserted in the 
hole. This bar is swung on a pivot in order that the tool can be 
made to follow the desired contour of the interior. 

Where the cavity is large and entails the removal of considerable 
metal, or where the forward or after fuse or plug hole is so small 
as to render machining impracticable, an entirely different process 
called noseing-in or bascing-in , as the case requires, is employed. 
Here the inner portion of the cavity is machined to size while the 
outer portion of the cavity is machined to a cylindrical or nearly 
cylindrical size, any shoulders or seats being also partially 
machined. The exterior surface of the projectile, in the wake of 
that portion of the cavity which is to be closed in, is then turned 
to the reverse curvature of the cavity, or in other words, the 
approximate contours of the cavity and outside are exchanged and 
reversed. That part of the projectile which is to be closed in is 
then carefully heated in a non-oxidizing flame, and is then either 
forced into a die, under hydraulic pressure, which is cut to the 


Projectiles 


525 


proper exterior shape, or is pressed into shape under radial pres¬ 
sure. As was stated above, this process can be applied to either 
the ogive or the base. Fig. 117 shows the various stages of pierc¬ 
ing, drawing and noseing of a 6 -inch army shell. 

This operation can be so satisfactorily performed that no 
machine work is necessary on the closed-in portion except the 
fitting of screw threads and gas-tight seats. 

It is generally customary to select tensile-test specimens from 
heats or lots after all forging or heating is completed, in order to 
insure that uniform and satisfactory results are being secured. 

The processes referred to above apply to practically all kinds of 
projectiles, except armor piercers and minor-caliber projectiles. 

Minor-caliber projectiles are generally machined from round 
rolled bars, the forging to shape with final finishing being more 
expensive than complete machining. 

Base plugs, fuse-hole plugs, adapters, and the miscellaneous 
interior parts of shrapnel, illuminating projectiles, gas and smoke 
projectiles, etc., are manufactured by the various drop-forging, 
drawing, and machining processes covered in text-books on 
mechanical processes. 

Special Projectiles. 

656 . Shrapnel (Fig. 118).—This type of projectile is designed 
for use against personnel and its only naval use is, therefore, in 



connection with landing parties, bombardment of fortifications 
and attack of aircraft. It is interesting to know that the name is 
derived from the inventor who brought it out in Europe in 1784. 

The most common form of shrapnel consists of a case in the 
rear of which is a black-powder bursting charge, connected to a 






















526 


Naval Ordnance 


nose fuse by a central explosion tube around which is packed a 
large number of lead (88 per cent)-antimony (12 per cent) balls 
held securely in place by a matrix of hot-poured rosin. When the 
fuse acts the balls are expelled forward by the bursting charge 
and scatter in a cone-shaped cloud. Shrapnel are, however, 
frequently given other features. For instance, a high explosive 
may replace the rosin to increase the violence of the burst and 
the area of damage; or there may be a heavv head with a high- 
explosive burster and suitable fuse in order to follow the cloud of 
balls with a secondary explosion. And finally the balls may be 
replaced by small hollow open-ended cylinders in which phosphorus 
or other incendiary compound is packed, the object of this design 
being to add to the local explosion and distribution of missiles the 
probability of creating a conflagration. This design is particularly 
valuable against aircraft of all descriptions, especially those which 
employ hydrogen. 

657 . Illuminating projectiles.—In this type we have a case, 
similar to a shrapnel case, with a very small burster in the front 
end just abaft the fuse, and an interior assembly of a star or 
candle with parachutes, and a very lightly held base plug. The 
explosion of the burster, or as it should be called the expelling 
charge, forces out the base and the interior assembly. It is quite 
desirable to expel the assembly with considerable velocity, at least 
300 to 400 f. s. relative to the case,* in order that it will have as 
small a velocity, in space, as is possible. It would be preferable to 
have the assembly expelled at the same velocity as the case is 
traveling, but at present this is not possible. The star or candle 
is a steel container in which is packed, under heavy pressure, an 
illuminating compound in which magnesium is an important con¬ 
stituent. The explosion of the expeller ignites the candle or star. 
The closed end of the star container is attached to a wire rope 
which carries a series of silk parachutes, the number depending 
on the weight of the star. These parachutes are carefully folded 
and they, and the wire, are so rolled that, upon expulsion, they 
open or come into action in succession beginning with the one 
nearest the star. The parachute nearest the star is quite small, 
only 4^ inches in diameter for a 3-inch projectile, and they increase 
in size until for a 5-inch projectile, for instance, the last parachute 
is about 3^ feet in diameter. The small parachutes are called 


Projectiles 


527 


retarding parachutes and the last and largest the sustaining para¬ 
chute. From this description the action of the assembly upon 
ejection is easily seen. The fast moving, heavy and burning star 
is gradually slowed down by the retarding parachutes, the opening 
of successive parachutes increasing the effective area and thereby 
maintaining a more or less constant retarding force, until by the 



Fig. 119 . —Illuminating Projectile Showing Projectile as 
Assembled and Descending Star. 

time the sustaining parachute unfolds it can open without danger 
of being torn to ribbons. This action is similar to that of a recoil 
brake. The wire for a 3-inch projectile is about 15 feet long and 
carries three parachutes, while in a 5-inch projectile the line is 
about 40 feet long and carries seven parachutes. The entire 
assembly gradually tails vertically and sinks earthward with com¬ 
paratively slow speed, the light of the star being thrown down- 










































528 


Naval Ordnance 


ward. As there is no need, with illuminating projectiles, for 
either great accuracy or a flat trajectory, fineness of exterior form 
is sacrificed to secure the maximum size and weight of star. 

658 . Smoke and gas projectiles.—These, when specially de¬ 
signed for the purpose, are quite similar to any high-explosive or 
Class B projectile so far as the projectile itself is concerned, the 
difference lying in the kind of fuse, contents, and method of 
loading. 




659 . Target projectiles.—Economy requires that target pro¬ 
jectiles be made of the least expensive materials. They are there¬ 
fore made of cast iron. A good grade of cast iron, and efficient 
methods of casting are necessary, however, to insure that the set¬ 
back and centrifugal force do not cause fracture, either in the gun 
or in initial flight. They are so designed that they are similar to 
their prototypes in exterior shape, weight and balance. No 
economy can be secured in the rotating band, as it must function in 
the normal way. 
















































Projectiles 


529 


660 . Proof shot, sometimes called “ slugs,” are solid cast-iron 
shot with a square forward end. From the forward edge of the 
rotating band to the rear, they are identical in shape with the 
standard projectile of their caliber, hut their only other similarity 
is their weight and bourrelet diameter. As a result of this design 
their behavior in the gun or interior ballistics is similar to, while 
their flight is much shorter than, that of the standard projectile. 
They are used for proving-ground work and spotting practices. 

661 . Marker projectiles.—A projectile similar to an illumi¬ 
nating projectile is fitted with a buoy in place of the star and 
parachute assembly and a water-impact fuse. The buoy carries a 
burning charge, principally compounds of phosphorus, which are 
ignited by the fuse, but which can not be put out by water. The 
burst expels this buoy, thus leaving a comparatively permanent 
mark of the position of the fall. This projectile is to indicate the 
position of hostile submarines to pursuing or hunting vessels. 

662 . Line-carrying projectiles.—These are simply loose-fitting- 
slugs which carry a rod extending to the muzzle with an eye in the 
end, to which is attached a light cord. The projectile turns around 
immediately after firing, and is held to its trajectory by the strain 
of the trailing cord. The cord is coiled down on deck and, after 
the projectile has passed over the target, a heavier line is bent to 
it and with succeeding heavier lines a hawser can finally be run. 
A range of about 350 yards can be secured in a 3-pounder saluting 

gun. 


35 


















■ 

























CHAPTER XVI. 


AMMUNITION AND AMMUNITION STOWAGE. 

PART I. 


Definitions. 


663. Ammunition is the general term applied to the assembled 
charges, cartridges, projectiles, etc., of all forms, used foi loading 
guns. It is of three kinds named from the purpose for which it 
is prepared, i. c„ " service,” “ target,” or " drill" All ammunition 
is of one of two types depending on the type of gun for which 


/ 


intended, “ case ” or bag ” ammunition. 

664 . Case ammunition is made up with the powder and primer 
contained in a brass cartridge case which fits the chamber of the 
gun snugly. The “ primer ” contains the " ignition charge.” The 
case is sealed by the projectile fitting into the mouth, or by a cork 
composition mouth plug', thus making it air-tight for the piotection 
of the powder. The former is called “'fixed case” ammunition 
and the latter “separate case” ammunition. All guns of 4-inch 
and below take “ fixed case ” ammunition, certain 4.7, 5 and 
6-inch guns take “ separate case ” ammunition and all other 

guns take “ bag ” ammunition. 

665 . The advantages of using case ammunition are: 

(a) Rapidity of fire. 

(b) Ease of handling, assembling and loading. 

(c) Charge safe from sparks in loading. 

(d) Less danger from flare-backs. 

(e) Less chance of double loading. 

(f) Cheaper to prepare. 

The disadvantages are: 

(a) Reduced chances for firing in case of misfire, as primer 

cannot be replaced. 

(b) Increased weight. 

(c) Danger from split cases. 

(d) Difficulty in loading in case of a loose projectile. 

666. Bag ammunition is that made up with the powder con¬ 
tained in one or more silk cloth bags with an ignition charge in 


53i 


532 


Naval Ordnance 


the base of each bag - . The primer is held in a firing lock screwed 
on the end of the mushroom stem. This type is made up in two 
ways, loose and stacked. In the former the powder is dumped 
loosely into the bag and the bag is then rolled and laced tightly to 
make a compact unit. In the latter, the powder grains are stacked 
in seried rows, each grain in a layer on end, and each layer placed 
successively in the bag and the bag sewed up and laced tightly. 
Stacked charges give a more compact, stiffer unit, easy to handle, 
occupying less space and eliminating a serious drawback in loosely 
packed bags, namely the cutting of the cloth by the sharp edges of 
the grains. Powder for service weights of charge for 12-inch 
guns and above, except the old 13-inch guns, is always stacked. 

667 . Ammunition details is the term applied to the component 
parts, exclusive of explosives, used in preparing ammunition and 
comprises the following: 

Primers. Projectiles. 

Cartridge cases. Powder bag cloth. 

Ammunition boxes or tanks. Distance pieces. 

Powder tanks. Wads. 

Fuses. Fuse covers. 

Tracers. Mouth plugs. 

Ammunition Details. 

668. A primer is a specially constructed device, the flame from 
which, when it is exploded by the direct action of the firing mechan¬ 
ism, ignites the powder charge in the chamber of the gun, and 
causes the explosion; either directly, as in case ammunition, or 
indirectly through the agency of the ignition charge, as in bag 
ammunition. This action is called the ignition. Smokeless powder 
is difficult to ignite with the application of a small flame. This is 
well shown by the ignition of a powder grain in air with a match, 
whereby it will be seen that the grain ignites slowly, burns rela¬ 
tively slowly and is easily extinguished. To provide a rapid and 
certain inflammation of the charge, an amount of black powder is 
used commensurate with the weight of charge and size of the 
smokeless-powder grain. Black powder has been found to be the 
substance best adapted for this purpose due to the rapidity and 
ease with which it is ignited, and the intense flame it gives off. As 
the function of the primer is to initiate the explosion, the design 


Ammunition and Ammunition Stowage 


533 


depends on the amount of ignition powder required and the form 
in which it is provided. 

669 . Types.—There are two general types of primers, one con¬ 
taining in itself the necessary amount of ignition powder, called 
the “ case primer,” and the other containing only sufficient black 
powder to direct a flame on to the ignition charge contained in 
the powder bag, called the “ lock primer.” Where it is necessary 
to increase the amount of ignition in a “ case primer,” the stock 
is lengthened to hold the additional black powder. The primer is 
then termed an “ ignition case ” primer to differentiate it from 
the short case primer. Primers may be divided in another way 
according to the method in which the ignition is initiated, as simple 
“ percussion primers ” where the flame is caused by the action of a 
hammer on a fulminate cap; simple “ electric primers ” where the 
flame is caused by the heating of a high-resistance wire igniting a 
wisp of guncotton; or a “combination primer combining both 
the above features. Formerly many types were issued to the 
service but they have been narrowed down now to three types for 
case guns and one for bag guns. They are (i) the percussion case 
primer, (2) the percussion case ignition primer, (3) the combina¬ 
tion case ignition primer, (4) the combination lock primer. 

Percussion fire only is provided for ammunition for 3~ffich guns 
and below and combination fire is provided for all above 3-inch. 
This division is made on account of the requirements for assembly 
and loading the ammunition and the handling of the gun. The per¬ 
cussion element is required for the larger guns in case of failure 
to fire electrically. 

670 . A percussion primer is loaded with a primer cap and a 
small charge of black powder depending on the size of the gun for 
which intended. An electric primer has in place of the cap a 
platinum bridge with a small wisp of dry guncotton wrapped on 
it. in an ignition chamber, which is filled with a mixture of pul¬ 
verized guncotton and fine black powder, and, in addition, a charge 
of black powder. The combination primer has both the cap and the 
platinum bridge so arranged that the flame from either will ignite 
the black powder. The primer cap composition usually contains 
fulminate of mercury. This substance easily explodes by per¬ 
cussion, friction, heating to 300° F., electric spark, or by contact 
with concentrated sulphuric or nitric acid. \\ hile weight foi 


534 


Naval Ordnance 


weight its explosive force is not much greater than that of gun¬ 
powder, it is very sensitive, especially when mixed with ground 
glass or sand. If is very sudden and positive in its action, as 
more powerful explosives of equal weight when substituted for 
it often fail to produce an explosion of the first order. It is never 
used alone as a cap filler but its explosive properties are moderated 
by the admixture of mealed powder, potassium nitrate or chlorate, 
or similar substance, while its sensitiveness may be increased by 
the addition of a small quantity of ground glass or similar sub¬ 
stance. The cap used in navy primers is known as a “ Winchester 
No. 2\” and contains 35 parts of fulminate of mercury, 35 parts 
of chlorate of potassium and 30 parts of sulphide of antimony. 

671 . An important phase of the service of a primer is the time 
interval in which it performs its function. The shorter the interval 
between the explosion of the primer cap and the ejection of the 
projectile from the gun the more efficient is the gun, for naval 
purposes in particular. Of this time interval a part is used up in 
the creation of a flame sufficient to start the inflammation of the 
powder, hence a primer must be suitably designed to obtain the 
best results. This accounts for the three different types used in 
case ammunition. If too much black powder is used, erratic pres¬ 
sures and velocities result, as is shown by the performance of the 
primer designed for a 4-inch gun when used in a 3-inch gun. In 
bag guns the primer interval is so nearly constant that the same 
type is suitable for all calibers. 

672 . Plate I, Fig. 1, shows a case percussion primer as used in 
the 1-3-6 pdr. and 3-inch low-velocity guns. It is simple per¬ 
cussion and contains only 45 grains of fine black powder, as this 
charge is sufficient to ignite efficiently the small powder charge 
required for these guns. It is assembled by forcing it into the 
primer aperture in the case, in a hand press. 

Fig. 2 shows a case percussion ignition primer as used in the 
3 / 5 ° §T n - It has 110 grains of fine black powder. It is screwed 
into the primer seat in the cartridge case. 

Fig. 3 shows the case combination ignition primer as used in 
4-inch ammunition and above for case guns. It has 265 grains 
of fine black powder, and both the percussion and electric elements. 
It is also a screw primer. 


SHELLAC 


CHAPTER XVI. PLATE I. 



Fig. i.—Percussion Primer. (For i-, 3-, and 6-pounders and 3-inch 

Field-Gun Cartridges.) 




one told or cream laid paper 

^COATED WITH SHELLAC 


KILL WITH ASBESTOS 
FIREPROOF PAINT 


two folos or cream 
LAIO PAPER 


BE CRIMPEO OVER 


ORNER TO 


"V 2i GRAINS HAZZAROS TFEG 
RIFLE POWDER L0A0E0 LOOSE 


ZFO GRAINS HAZZAROS FTfG 
RirLE POWDER LOAOEO LOOSE 


Fig. 3 _Case Combination Ignition Primer. 


-PRIMER STOCK 




THIS primer contains 

40 CRAINS OF HAZARDS 
RIFLE POWDER FFFG GRADE 
IGNITION COP NUT 
IGNITION CUR— 

-WAD BRISTOL BOARD PLUNGER CUf 





ASBESTOS FIRE PROOF TAINT 

WINCHESTER PRIMER 

Fig. 4.—Combination Lock Primer. 

PRIMERS. 


BE CRIMPED 















































































































536 


Naval Ordnance 


673 . The essential features of the case ignition primers are the 
extension magazines holding the ignition charge, the ignition tube 
and the screw thread. The extension carries the ignition into the 
center of the powder charge and when exploded directs the flame 
outward through the holes in the extension into the body of the 
powder charge. The interior brass tube, called the ignition tube, 
contains a small charge of from 2 \ to 3^ grains of black powder 
and acts as a train between the cap and the ignition charge. The 
holes in both tubes are sealed by manila paper tubes and shellac. 

Fig. 4 shows the combination lock primer containing only 
30 grains of black powder. The method of insulation to form a 
circuit is shown clearly by the heavy black lines. 

Simple electric primers or simply percussion lock primers may 
be met with in service but they are remnants left from previous 
stocks and are for drill and test purposes only. A special short 
case percussion primer is used for “ non-recoil ” gun ammunition. 

Cartridge Cases. 

674 . The powder charge for some guns is put up in brass 
cartridge cases, which are hollow cylinders with flat heads, shaped 
to fit the chamber, those for late guns being bottle necked. The 
head has a rim for the extractor and a central aperture for the 
primer. The cases are drawn from solid disks in successive passes 
in hydraulic presses equipped with suitable dies. Tbe disks, 70 per 
cent copper and 30 zinc, when cast are very malleable and ductile 
and roll easily. The metal is bright yellow in color. Each case 
is carefully gauged, after machining, to ascertain that all dimen¬ 
sions may be within the tolerances allowed. It is of the greatest 
importance that each case should be interchangeable, that the 
extractor fits the rim, the primer fits the seat, the projectile fits 
the mouth, and that the length be correct so that the assembled 
charge will fit the gun. 

Cartridge cases are reloadable, when they have been cleaned 
and reformed after firing. To reduce the preparatory work pre¬ 
vious to reloading, the navy regulations state explicitly how they 
shall be handled after use. They are required to stand six service 
rounds without deterioration before acceptance from the manu¬ 
facturer. This fact is established by firing a number from each 
lot at the proving ground. It frequently happens that cases will 
stand from 30 to 40 rounds before becoming useless. 


Ammunition and Ammunition Stowage 


537 


The head of the case has an internal boss in the center which 
is drilled out and, when designed to take an ignition primer, the 
hole is tapped. It is of the greatest importance to have this 
aperture exactly concentric in order that the primer will be aligned 
with the firing pin. The depth of seating must be exact in order 
that the primer will be inset the required amount. If the primer 
is inset too much a misfire will occur, and if it is not inset a suffi¬ 
cient amount it is a source of danger in the event it is struck 
against a sharp object. 



675 . Non-recoil guns require special cartridge cases. These 
guns are used where it is desired to keep the recoil at a minimum. 
Where brass cases are used, the recoil charge is assembled m the 
rear as a part of the case. In one type, where it is desired to 
eliminate unloading, a steel case is used with a rotating band on 
the end of it. When the gun fires, the case is propelled to the 
rear and acts as a projectile, the rotating band preventing ga^ 
escape. The propellent charge is carried in this case and the 
assembly is the same as for regular ammunition. A special feature 
is the number of rings similar to the bourrelet of a projectile with 
holes through the case covered by shellacked paper. 1 hese holes 
permit the gas to escape so that the pressure is on the walls of the 
gun, thus preventing binding in the bore. As the firing lock is on 
the side of the gun the primers are assembled through the side o 
the cases. Special short primers are provided. A lug on the case 
engaging a slot in the gun admits of loading so that the primer 

will be in position opposite the firing pin. 

Plate II shows the steps in the manufacture of a cartridge case. 

Plate III shows cases of different sizes. 

Fig. 122 shows non-recoil gun ammunition assembly. 




































CHAPTER XVI. PLATE II. 



STEPS IN DRAWING FINISHED CASE FROM THE “BLANK. 







































CHAPTER XVI. PLATE Ilia. 



CARTRIDGE CASES. 


























CHAPTER XVI. PLATE 111 b. 















Ammunition and Ammunition Stowage 


54i 


Ammunition Tanks and Boxes. 

676 . Case gun ammunition, after it is prepared, is packed in 
tanks or boxes for issue to the service. This is necessary for its 
safe transportation and stowage. Standard containers are used 
varying in size and capacity with the caliber of the ammunition. 
As many cartridges are packed in a container as will allow easy 
handling. 

4 -inch and above . 

3"/50 . 

3”/23 . 

6 -pounder . 

3 -pounder . 

i-pounder anti-aircraft 
i-pounder . 

677 . As the ammunition is stowed in a magazine remote from 
the guns, the containers must be strong enough to stand consider¬ 
able handling, especially that which they undergo in passage up 
the ammunition hoists. The boxes are made of soft pine with 
one or more rope grommets for ease in handling. I he tops are 
either loose and held in place with marline, or hinged and clamped. 

678 . Suitable racks or nests are provided in each box with 
wooden blocks to protect the ends of the cartridges and to hold 
them rigidly in place. Ammunition boxes, being- of wood, are 
subject to easy destruction and are not water-tight. In con¬ 
sequence, the tendency in recent years has been to replace them 
with metal tanks. As the projectile or primer may leak the car¬ 
tridge case cannot always be relied upon to remain air-tight, so 
that the present practice is to make the tanks airtight. This gives 
the additional advantage of good stowage in “ ready service 
racks on deck, where the ammunition is exposed to the weather. 
The tops are fitted with rubber gaskets and are secured by a lug 
and butterfly nut. The tanks are usually circular in cross-section, 
thereby changing the stowage arrangements from boxes, which are 
all rectangular in shape. The tanks are made fiom sheet metal 
with brass top and bottom rings. The body is galvanized after 
completion. The top and bottom rings are made strong enough 
to permit of stacking without the use of racks. Metal tanks are 
used for 4V50 ammunition, and 3750 and 3723 for submarines. 


one per box or tank 

four “ “ “ “ 

six “ “ “ “ 

eleven “ 

sixteen “ 

one hundred per box 
sixty per box 









CHAPTER XVI. PLATE IVa 



TYPES OF CARTRIDGE BOXES. 





















CHAPTER XVI. PLATE IVb. 



TYPES OF CARTRIDGE BOXES. 












544 


Naval Ordnance 


Before acceptance, the tanks are required to stand an air-pressure 
test. Before issue to service, containers are painted and tagged to 
show their contents. 

Plate IV shows different types of boxes. 

Plate V shows different types of ammunition tanks. 


Powder Tanks. 

(Plate VI.) 


679 . Powder charges for bag guns are stowed in sheet steel or 
copper tanks. The considerations in the design of a powder tank 
are: 


(e) Stowage facilities. 

(f) Handling facilities. 

(g) Capacity. 

(h) Nonacid surface inside. 


(a) Airtightness. 

(b) Strength. 

(c) Lightness. 

(d) Quick opening. 


680 . As smokeless powder changes its ballistic properties when 
exposed to air, it is essential that the containers remain airtight, 
while in use for storage of powder. To effect this, the tank closure 
is fitted with a rubber gasket on which the cover is forced by 
various systems of dogs and nuts or cams, either fitted on the 
outside of the tank or contained in the cover itself. Self-contained 
closures with the necessary dogs not projecting beyond the limits 
of the body of the tank are considered more desirable, as there 
is less likelihood of loosening the cover, thereby causing a leak. 
The standard test for airtightness is to hold 5-pounds pressure for 
three minutes. 

Plate VI, Figs. 3 and 5, shows dogs fitted on the outside; Figs. 2 
and 4 show a self-contained closure. 

681 . Powder tanks mu t be strong enough to stand the neces¬ 
sary handling in stowage below and, in case of broadside guns, in 
handling in the ammunition hoists. They are designed with 
sufficient strength to withstand normal stresses but should never 
be subjected to knocks which may result in leaks. The main 
strength is placed in the top and bottom 1 ngs in order to permit 
stacking. Copper tanks are strengthened by wooden battens on 
the sides. Handles riveted to the sides are a source of weakness 
due to the pulling loose of the rivets when handling the tanks 
loaded. 


CHAPTER XVI. PLATE VI. 


1 



Fig. i.—B ottom of Tank. 



Fig. 2.— 6-Inch Tank, Mark VII. 


Fig. 3.—12-Inch Tank. 


POWDER TANKS. 



DESIGNS OF POWDER TANKS. 












































































































































































CHAPTER XVI. PLATE 





36 


TYPES OF CARTRIDGE TANKS. 












CHAPTER XVI. PLATE Va. 











TYPES OF CARTRIDGE TANKS. 















548 


Naval Ordnance 


682. The design of all tanks is such as to contain the charge 
with the least amount of waste space, hence the cylindrical form 
has been adopted, as requiring the least amount of metal, the 
smallest closure, and, except in case of rack stowage, the least 
stowage space. The inside dimensions of a powder tank should be 
such that it will be a gauge for the charge, so that charges which 
fir the tank will fit the guns. To provide for uniformity in load¬ 
ing, it is considered desirable to have the total length of charge 
bear a fixed relation to the length of chamber. The length of 
the several sections when placed end to end, as they would be in 
the gun, should be about two inches less than the distance from 
the mushroom face to the base of the projectile when seated. This 
condition is not obtained for all guns in service, due to the design 
of old tanks. 

683. In order to sustain a good rate of fire it is necessary to 
have the tanks so designed that the covers can be quickly and 
easily removed. As it is forbidden by regulations to open more 
than one charge per gun at a time in a magazine or gun com¬ 
partment during firing, or to loosen a cover so that more than one 
charge is exposed during firing, it is desirable to have the least 
number of men employed in keeping the rate of supply equal to the 
rate of fire. Special wrenches are provided for the removal of 
the tank covers. 

684. Special handling facilities are provided for lifting and 
transporting powder tanks, either as a bail fitted to the cover, 
or as handles on the sides. The handling arrangements should be 
such that no injury will result in developing leaks, and in all cases 
the bail or handles should be fitted to the strong part of the tank. 
Handles fitted to the sides do not fulfil this condition, and will not 
be provided in the future; instead, slings around the top ring will 
be used. 

685. Tanks are stowed in tiers, either in racks or loose stacked. 
When loose stacked they must be designed so that the stronger 
parts will take the weight and so that projections do riot interfere. 
Each tank must be so strong that the weight of those piled on 
top of it will not deform it sufficiently to cause a leak or jam the 
cover. When tanks are stowed in racks these conditions do not 
have to be fulfilled. 


Ammunition and Ammunition Stowage 


549 


686 . The size of the individual tank should be such that it will 
contain the largest fraction of the charge and still not be too 
cumbersome for easy handling. Up to 8 -inch the entire charge 
is contained in one tank, from 8 -inch to 16 -inch two tanks are 
required per charge; for i6"/45 two and one-half tanks are re¬ 
quired, and for i6"/5o three tanks are required. A tank weighing 
loaded three hundred pounds is considered to be a maximum for 
ease in handling. The fewer tanks to be used means the fewer 
closures and the fewer opportunities for leaks and chances for 
deterioration of the powder. 

687. As a protection for the powder, the interior of a tank 
must be neutral, clean, dry, and free from dirt. Sheet-steel tanks 
are painted on the inside with non-acid paint. Tanks constructed 
by soldering or sweating are treated with alkali water and 
thoroughly cleaned with fresh water. As a protection to the 
ignition pad, a sheet of clean manila paper is placed in the 
bottom of the tank. 

Plate VI shows the general features of powder tanks. As there 
are many types in service no attempt will be made to describe any 
in particular. 

Fuses. 

688 . A fuse is a device which, when exploded by the action of 
its mechanism, ignites or detonates the burster charge of the 
projectile either on or after impact, or in flight. A fuse function¬ 
ing on impact is a “percussion” fuse; one functioning after a 
definite time in flight by its own internal action is a " time " fuse. 
Certain types combine the features of both these and are called 

time percussion ” fuses. 

689. A fuse must (a) be safe in assembling, handling, trans¬ 
porting, loading and firing, (b) not function prematurely, (c) be 
positive in its action, (d) not be subject to deterioration in storage. 

690. A fuse is said to be armed when, by the action of its 
mechanism, the firing point is in a position to impinge on the cap 
with any forward motion of the plunger. 

691. The set-back” is the action which occurs when the pro¬ 
jectile starts to move. That is, the inertia in a movable part will 
cause it to lag behind the fuse stock which is rigidly attached to 
the projectile by the fuse threads. 1 he oeep is the action of a 


550 


Naval Ordnance 


movable part inside the fuse due to the retardation of the pro¬ 
jectile in flight from air resistance. That is, the part will tend 
to move forward, as the air resistance does not affect it. 

692. Fuses as originally used in spherical projectiles were 
“ time,” or “ concussion ” fuses. No entirely satisfactory “ per¬ 
cussion ” fuses were ever developed prior to the use of rifled guns 
and elongated projectiles. 

693. The oldest form of time fuse was a piece of “ fusee ” or 
“ slow match.” This was followed by a wooden fuse forced into 
the opening in the shot, containing a compressed black powder 
charge, which was ignited by the blast of the gun and when burned 
down to the end spit through an opening into the burster charge 
and exploded the projectile. The wooden fuse was cut off or 
pierced along its length to fix the time of burning. In later devel¬ 
opments, metal cases were substituted but the principles involved 
were the same. In a concussion fuse, an inflammable composition 
was ignited on discharge of the gun and, on impact, by some con¬ 
trivance, the flame was admitted to the burster charge. The con¬ 
trivances used were glass tubes, zinc tubes, which when heated by 
the burning powder inside would break off on impact, or by plaster 
of paris tubes. Due to the fact that a spherical projectile would 
strike on any point of its surface, percussion fuses did not operate 
satisfactorily, though tried in many forms. In one type three 
distinct double-ended plungers were used with their axes perpen¬ 
dicular to each other. The plunger, whose axis was in line on 
impact, was arranged to strike a fulminate composition. The 
plungers were held in place during flight by copper shear wires. 

694. On the introduction of rifled guns and elongated pro¬ 
jectiles, the troubles with percussion fuses were largely eliminated, 
and as the projectile always struck point first, the use of the motion 
of a plunger striking a cap on impact was made possible. The 
adaptation of the rotation of the projectile to additional safety 
features marked the further advancement in the design of fuses. 
With the modern use of high explosives a further change was 
required in providing a detonating element and in producing a 
delay action feature. 

695. All percussion fuses act by the forward motion of a 
plunger in the fuse body, caused by the sudden arresting of the 
motion of the projectile. The plunger carrying the firing point 


Ammunition and Ammunition Stowage 


55 f 


strikes a primer cap; or else, carrying the primer cap, causes it to 
impinge on the firing point which is held rigidly in place in the 
fuse body. 

696. A “ percussion fuse ” may be either an ignition fuse for 
exploding a black-powder charge or a detonating fuse for detonat¬ 
ing a high-explosive charge. A percussion fuse may be designed 
to fit into the base or to fit the nose of the projectile. 

697. In the simpler and older types of percussion fuses, the 
plunger was held in a safe position by split rings or by shear 
pins. The action of “ set-back ” on discharge caused the plunger 
to shear the pin or to ride over the split rings and then be in a 
position to move forward on impact. This was the first form of 
safety device. It proved insufficient for complete safety as one 
blow would arm the fuse. To obviate this difficulty advantage was 
taken of the rotation of the projectile to provide centrifugal safet\ 
locks on the plunger to keep the firing point away from the primer 
cap until the projectile had attained sufficient rotational speed 
in its passage down the bore. Refinements were then added to 
prevent complete arming until the projectile had left the muzzle. 
A premature discharge in the bore would cause a tremendous 
amount of damage. 

698. The conditions for safety may be summarized as follows; 

(a) Fuse must not be armed when dropped or joggled. 

(b) Fuse must not function on set-back. 

(c) Fuse must not function in bore. 

(d) Fuse must not function prematurely in flight. 

699. The centrifugal weights are held in place by small springs 
and are usually duplicated so that a knock on either side will only 
dislodge one and even then it will be replaced at once by the spring. 
The motion of “ set-back ” tends to carry the firing point away 
from the primer cap so no difficulty is found in this respect. 1 lie 
weights of the centrifugal parts are so designed or the relative 
motion of the parts so prevented that the final arming is not 
effected as long as the projectile is subjected to the accelerating 

force. 

700. There is a tendency for the plunger to creep during the 
flio-ht as it is not subject to the same retardation as the projectile 
due to the air resistance. This will cause the plunger to move 
forward and leave the firing pin in contact with the primer cap. 


552 


Naval Ordnance 


A light spring forward of the plunger is introduced to obviate this 
difficulty. 

701. The Semple centrifugal plunger illustrates the safety 
features as now found in fuses. This mechanism is used by many 
fuse makers for a number of governments. It is patented in many 
countries. As certain other features of our fuses are confidential 
the plunger action only will be explained. The mechanism, Plate 
ATI, consists of the firing pin 2 , plunger body 1 , safety pins 3 , 
safety-pin springs 4 , firing-pin axis 5 and the creep spring 6 . In 
the safety position Fig. 1 the safety pins are pressed against the 
firing pin in its safe position, by the small safety-pin springs 3 . 
A side blow would dislodge only one of them so that the fuse is 
safe from side impact. The fuse is safe from drop for the firing 
point is housed in the plunger. When rotated the safety pins are 
forced out against the action of their springs and the firing pin for 
the same reason rotates on its axis, bringing the firing point into 
the armed position. The inertia in the firing pin will cause it to 
lag during the acceleration of the projectile until the projectile 
leaves the gun, at which time the firing pin assumes the position 
shown in Figs. 2 and 3 . Before assembling the plungers in the 
fuses they are tested in a clutch driven by a motor and must arm 
at a predetermined number of revolutions, varying from 1300 to 
3000 R. P. M. 

702. Certain detonating percussion fuses are provided with a 
delay action element so as to permit the projectile to pierce and 
detonate behind armor. Some ignition fuses are so designed as to 
function on graze for land work or on water impact. The fuse 
stocks are made in two sizes, one for minor-caliber projectiles, 

3 - inch and below, and the other for medium-caliber projectiles, 

4 - and 5 -inch. Detonator fuses are used for 6 -inch and above. 

703. I he time fuse depends on the burning interval of a 
specially prepared slow burning powder compressed into a groove 
or ring. This composition is carefully mixed to render it as uni¬ 
form as possible, in order that equal lengths will be consumed in 
equal time intervals. When the powder has burned to the end of 
its train, the flame ignites the fuse magazine charge and then the 
burster charge, exploding the projectile instantly. The setting of 
the fuse determines the length of powder train which will burn, 
hence the time interval to the burst. Formerly, time fuses were 


CHAPTER XVI. PLATE VII. 



SEMPLE CENTRIFUGAL PLUNGER. 



































































554 


Naval Ordnance 


ignited by the flame from the powder charge of the gun, as it came 
in contact with the exposed powder train, which was cut for the 
desired time interval. In the present high-powered guns, it has 
been necessary to use a primer action. The powder train is ignited 
by the flame from a primer cap which is struck by the action of the 
plunger moved either by set-back on discharge of the gun or by the 
rotation of the projectile. , 

704. The following conditions affect the uniformity of action 
in time fuses with the powder trains: 

(a) Age of fuse. 

(b) Hygroscopic condition due to storage. 

(c) Barometer pressure. 

Old compositions burn more slowly than new ones due to 
chemical changes in the constitutents of the composition. 

Black powder is very hygroscopic. Fuses stored in a damp 
atmosphere will permit the composition to take up moisture and 
cause it to burn slowly. If they are stored in a warm atmosphere, 
the composition will dry out and burn faster. 

Increased atmosphere pressure causes the powder train to burn 
faster, while decreased pressure causes it to burn slower. This 
change in rate of burning has become a matter of prime importance 
in anti-aircraft firings. There are two reasons given for the 
change in rate of burning with change in atmospheric pressure. 
Each layer in the train is ignited by having its temperature raised 
by the gases of combustion of the layers above it. With decreased 
atmospheric pressure the gases expand more freely and conse¬ 
quently are not in such close contact and, furthermore, by the 
increased expansion cool more rapidly, causing a decreased rate of 
burning. 

Tbe size of the projectile affects the rate of burning in that the 
loss of velocity for larger projectiles is less; hence the change in 
pressure on the fuse is less and the powder train burns quicker. 

On account of these disadvantages clockwork time fuses are 
being adopted but their details are not published. 

The Frankford Arsenal 21 -second time percussion fuse is the 
one generally used for shrapnel. An adaptation, the Scovill time 
fuse, having the time element only is used for anti-aircraft work. 

705. Frankford Arsenal 21-second combination fuse.—This 
fuse is shown in Plate VIII. Most of the parts are made of 


CHAPTER XVI. 


PLATE VIII. 




/.r-At- thos. p. /. p. H. 




Fig. i.—E xterior. 



Fig. 2.—Before Arming. Fig - 3-—After Arming. 

ANKFORD ARSENAL 21-SECOND COMBINA flON FUSE. 













































































































556 


Naval Ordnance 


bronze. There are two time-train rings, c and d, and an annular 
horseshoe-shaped groove is milled in the lower face of each ring. 
Meal powder is compressed into these grooves under a pressure of 
70,000 pounds per square inch, forming a time train, the total 
length of which is 7 inches. 

The time element of this fuse is composed principally of the fol¬ 
lowing parts: the time-plunger e, the split-ring spring e', the 
hring-pin f, the vent g leading to the upper time train i, the com¬ 
pressed powder pellet h, the lower time train k, the compressed 
powder pellet m, in the vent o, leading to the powder magazine p. 

The upper ring c is prevented from rotating by the pins x. 

The vent g is drilled through the walls of the time-plunger 
chamber, and is exactly opposite a hole in the inner surface of the 
upper time train leading to the end of the train from which the 
direction of burning is anti-clockwise. The hole j is drilled 
through the upper face of the lower time-train ring d, to the end 
of the lower time-train groove from which the direction of burn¬ 
ing is clockwise. 

The lower time-train ring is movable, and is graduated on its 
outer edge in a clockwise direction from o to 21 , each full division 
corresponding to one second of time of burning in flight; these 
divisions are subdivided into five equal parts, each corresponding 
to one-fifth second. A radial hole is provided in the lower ring 
for a pin to be used in setting the fuse. An arrow on the lower 
flange of the fuse stock is the datum line for settings. 

The vent 0 is drilled through the flange of the fuse stock to the 
powder magazine p, and leads to the same end of the lower time 
train as the vent j —that end from which the direction of burning 
is clockwise when the fuse is at its “ zero ” setting. 

The action of the fuse as a time fuse is as follows: Assume 
first the “ zero ” setting as shown in the figure. The time plunger, 
a ring-resistance plunger, arms on the stock of firing. The flame 
from the primer passes out through the vent g, igniting the pellet 
h, to the end of the upper time train i; and down through the vent 
j, to the end of the lower time train k; and thence through the 
vent 0 , to the magazine p. 

It will be seen that for the “ zero ” setting of the fuse the 
origins of both upper and lower train are in juxtaposition. As¬ 
sume any other setting, say 12 seconds. The vent j has now 


Ammunition and Ammunition Stowage 


557 


changed its position with respect to the vent h, leading to the 
beginning of the upper time train, and the vent o, leading to the 
powder magazine p, both of which points are fixed by the angle 
subtended between the “ zero ” and the 12 -second settings. The 
flame now passes out through the vent g and burns along the 
upper time train in an anti-clockwise direction until the vent j is 
reached, when it passes down to the beginning of the lower train 
and burns back in a clockwise direction to the position of the 
vent o, whence it is transmitted by the pellet m to the magazine p. 

For the 21 -second setting the flame burns the length of both 
trains. As the trains do not extend all around the fuse, the solid 
part between the ends of the trains is utilized to obtain a safety 
setting. When this point, marked S, is brought opposite the arrow 
on the lower flange of the fuse, the vent j is covered by the solid 
metal between the ends of the upper train, and the vent 0 is cov¬ 
ered in a similar manner by the lower or movable ring. 

The percussion element consists of the primer r and the new 
centrifugal plunger q. The plunger is in two parts held togethei 
by the bolt ( 1 ), and spring ( 2 ). When the fuse attains 2500 
revolutions, the plunger opens out and the cross-pin ( 4 ) pulls the 
point ( 3 ) to an upright position, so that upon impact the plunger 
will fly forward and the point will strike and explode the primer. 

706. Time fuses are covered with thin brass covers held on by 
soldered strips. These are removed by tearing the strip prepara¬ 
tory to setting the fuse. Rubber covers are provided in case the 
round is not fired. It is of the greatest importance to keep fuses 

dry for the reasons given above. 

New time fuses require special fuse setters, the details of which 
are published in pamphlets issued by the Bureau of Ordnance. 

Tracers. 

707. A tracer is a device fitted on a projectile to make it 
possible to follow it in flight. There are two kinds, the day tracer 
for anti-aircraft work and the night tracer for general use. A 
tracer may be incorporated in the same stock as the base fuse, in 
which case it is called a tracer fuse. However, both are distinct 

and independent of each other in action. 

In a day tracer, a trail of black fluid or smoke is left by allowing 
the fluid to be thrown out by centrifugal force or by the products 
of combustion of the tracer compound. 


558 


Naval Ordnance 


In the night tracer, the illumination is accomplished by means of 
a highly compressed slow burning composition ignited by a fric¬ 
tion element or by a percussion cap. In the former type there is 
a small air chamber in the mouth of the tracer covered by a metal 
disk in which is cut a gas port. The cover is connected to the 
friction element by means of a rod. (Plate IX, Fig. i.) 

708. The action of the tracer is as follows: On explosion of 
the smokeless-powder charge of the gun, the gas of the charge 
enters the tracer chamber through the gas port; and, while the 
projectile remains in the bore of the gun, the gas in the tracer 
chamber is under high pressure. After the projectile leaves the 
gun, the pressure on the tracer port being released, the cover of 
the tracer is forced to the rear by means of the expansion of the 
gas in the chamber. The forcing of the cover to the rear draws the 
central rod to the rear and ignites the friction element, which, 
in turn, ignites the slow-burning composition of the tracer. This 
composition burns from 12 to 15 seconds, depending upon the 
design of the tracer. 

In the latter type the ignition is effected by the action of a firing 
pin on the cover acting on a primer cap. 

Plate IX shows different types of tracers. 

Tracer mixtures are confidential. 

Projectiles. 

709. The manufacture of projectiles is treated in Chapter XV. 
As an ammunition detail, the main concern is the loading and fus¬ 
ing of a projectile. The explosives used are high explosives or 
black powder. The cavity of a projectile must be especially pre¬ 
pared to receive the burster charge by treating it with a coat of 
non-acid paint, in order that no sensitive combinations may be 
formed with the explosive used. The burster charge may be of 
picric acid or one of its compounds, TNT, ammonium nitrate, 
tetryl, black powder, or combination of any of these. In U. S. 
Navy projectiles explosive “ D.” TNT, or black powder is used, 
all of which are stable under ordinary conditions of storage. 

710. The purpose for which a projectile is to be used fixes the 
kind of burster charge and the type of fuse. The degree of frag¬ 
mentation is fixed by the character of the burster charge. In 
armor-piercing projectiles, which are very tough, a high explosive 


CHAPTER XVI. PLATE IX. 




Pig. i. —Target Tracer for Minor-Caliber Projectiles. 





Fig. 2 . —Tracer Fuse for Minor-Caliber Projectiles. 



BASE OF SHELL 



GRAMS 



WT. TWO 
TRACERS 


/0 


WT. TWO 
85 GRAMS TRACERS 
162 GRAMS 


Fig, 


WT H70 GRAMS 

3.—Tracers (3. 4, 6. 7, 9 and io) and Tracer Fuses (5 and 8). 
TRACERS AND TRACER FUSES. 
















































































































































































560 


Naval Ordnance 


is required. In common projectiles, the proper fragmentation is 
obtained by mixing a high explosive with black powder. The high 
explosive in this case is not detonated but gives a low-order detona¬ 
tion, that is, the high explosive is consumed by burning rather 
than by changing instantaneously into the gaseous state. A high 
explosive in a common projectile, if detonated, would break the 
metal up into such small pieces that it would not be effective. In 
Class B projectiles, where the explosive force of a large quantity 
of high explosive rather than the damage from fragments is 
desired, TNT is used. In shrapnel and illuminating projectiles, 
where the object is to discharge the contents of the projectiles, 
small black-powder charges are used. Flat-nose projectiles are 
loaded similarly to Class B projectiles. 

711. When gas loaded, some of the explosive charge is omitted 
and replaced with a container either of cotton duck or metal hold¬ 
ing the gas mixture. On burst the gas mixture is diffused in the 
atmosphere. Various kinds are in use, some of a very poisonous 
nature, but the details of preparation are confidential. 

The following table shows the assembly of projectiles: 


Projectile. Designation. Burster charge. Fuse. 

Armor piercing... A. P. Explosive “ D.” Delay action detonating. 

Common . C. Black Powder, Ignition percussion. 

TNT or “D.” 

Shrapnel . Shrap. Black Powder. Time percussion. (For 

A. A. time only.) 

Illuminating . S. S. Black Powder. Time. 

Class B. Cl. B. TNT. Time percussion detonat¬ 

ing. 

Flat nose. F. N. TNT. Sensitive percussion de¬ 

tonating. 


Any of the above fuses may have a tracer element, or a tracer 
fitted in the base. 

i t . * 

Base plugs are described under the manufacture of projectiles. 

Powder Bags. 

712. The charges for powder bag guns'are prepared by placing 
the powder in bags made of special silk cloth, sewed with silk 
thread and laced with a silk cord. The object in using silk instead 
of a less costly material is to reduce the danger from unconsumed 







6'" 50 CAL. FC 


CHAPTER XVI. PLATE X. 




Fig. i. 



i 


HANDLING STRAPS 


(fc=5 

< 

-X 

X 


O 

in 

X 


id 

'T LL’. 

X 


o- 1 ’* 

X 


i . 

X 



- . . 



XgNITION POCKET 

THIS END DYED 
CARMINE RED. 



Fig. 3. 


CARTRIDGE BAGS. 


37 







































562 


Naval Ordnance 


smoldering residue. There are two weights, light and heavy. 
The body of the bag is made from the heavy in order to withstand 
better the necessary handling, permit of tight lacing, hold the 
required weight and reduce the tearing due from cutting by the 
edges of the grains. The light weight is used for the ignition ends 
where it is required to hold no weight and where it is desired to 
have the flame from the primer burn through readily. Plate X 
shows the details of powder bags. 

713. The following conditions must be fulfilled by powder bag 
cloth: 

( 1 ) Strong enough to stand handling and transportation, espe¬ 
cially the wear and tear of movement in tanks due to the motion 
of the ship. 

( 2 ) Close weave to contain the powder, especially if dusty. 

( 3 ) Permeability to flash for combustion. 

( 4 ) Ability to withstand chemical changes in case of reactions in 
the powder. 

( 5 ) Must be entirely consumed. 

( 6 ) Free from acids which may react on the powder. 

714. On one end the ignition charge is attached, made by en¬ 
closing in a circular bag of thin silk cloth the required amount of 
black powder, then quilting the sides together to form the ignition 
pad. The face of this ignition pad, which is to be on the outside, 
is made from silk cloth previously dyed red. The pad is then 
sewed to the bottom of the bag. The other end of the bag is fitted 
with a strap for handling, sewed to the front end with extensions 
down the side. These straps are strongly made to withstand the 
required handling in withdrawing the bag from the tank and in 
the successive steps in loading the gun. In order to make a com¬ 
pact package, two flaps with eyeholes at intervals are sewed down 
the side at such a distance apart that when laced together by a 
silk cord enough space will remain to permit of taking up any 
slack which may result from further shaking down of the charge 
in service or from any stretch in the material. 

715. Distance pieces and wads.—Formerly powder bags were 
used with case ammunition, the bags, fitted with an ignition pad, 
being loaded with the powder charge and assembled in the 
cartridge case. The space between the bag and the projectile was 
filled with excelsior. With the advent of the ignition primer the 


Ammunition and Ammunition Stowage 


563 


interior bag has been omitted, and cardboard disks and distance 
pieces are now used in place of excelsior. Disks are cut slightly 
larger than the diameter of the case and slit down from the edge 
to the center. Distance pieces are made by crossing and locking 
four pieces of cardboard in a manner similar to that used in com¬ 
mercial life for crates. The distance pieces are cut to the desired 
length depending on the amount of powder used. Felt wads, cut 
to the size of the case, are used in place of distance pieces when 
the charge fits the case snugly, or when saluting charges are 
prepared. 

Mouth Plugs. 

716. With separate case ammunition, it was formerly the prac¬ 
tice to seal the case with a brass mouth cup. This was in the 
form of a brass bowl, the sides of which fitted inside of the case. 
The object in its use was twofold, first to form a gas seal in the 
case to prevent escape of the gases past the rotating band, also to 
keep gases from breaking cases by outside pressure on the case, 
before the projectile started to engrave the band in the grooves, 
and, second, to make the case an air-tight container for the powder 
charge. It has been shown that the gas escape is insufficient to 
require this form of seal and as the brass mouth cup had a 
tendency to break up and boomerang back, so as to endanger per¬ 
sonnel, cork plugs have been substituted, and these effectively 
protect the powder. 

Assembly of Ammunition. 

717. Ammunition details are received at ammunition depots 
from the manufacturers after proof and stored until required for 
assembly for issue to the service. When orders are received for 
the preparation of ammunition, the projectiles are loaded and 
fused, the powder charges assembled, the ammunition packed and 
marked and prepared for delivery to the ship, in such a condition 
that no further work is required on it. 

718. Projectiles are loaded as a separate operation. Each one 
is cleaned, gauged, inspected, and then loaded with the proper 
explosive. Black powder or the mixed filler is loaded in loosely, 
explosive “ D ” is loaded under pressure in hydraulic presses and 
TNT is loaded either loosely, under pressure, - or in the cast 




564 


Naval Ordnance 


form. After the explosive is loaded the projectiles are removed 
to a separate room where the fuses are carefully assembled and 
the projectiles are then painted to show the type of explosive. The 
loading of shrapnel is a special operation treated under Projectiles. 

Projectiles for bag guns, when issued to the service, have 
special grommets fitted over their rotating bands. These are 
supplied when the projectiles are delivered by a manufacturer and 
are intended to prevent burning of the band, knocking it loose, 
etc. Formerly, they were made of fiber, but the recent design is a 
canvas belt with a rope grommet abaft the band, the whole being 
held in place by a marline lashing. 

719. In assembling case ammunition the cases are inspected, 
cleaned, gauged and then the primer is inserted. Case percussion 
primers are forced into place by hand or machine presses and case 
ignition primers are screwed into place. Care is taken to see that 
the primer has the proper seating, neither projecting nor inset 
too far. The predetermined weight of powder is then weighed 
out on carefully checked scales and poured into the case. A wad 
is then forced in to keep the powder in position around the primer, 
a distance piece is then placed on top of the wad and another wad 
is placed on top of the distance piece. The case is then placed in a 
press, the base of the loaded and fused projectile is entered in the 
mouth of the case and forced in until the rear of the rotating band 
takes up against the mouth of the case. The cartridges are then 
packed in containers with great care to obviate any movements in 
transit or possibility of damage to the nose fuse, if of that type. 

720. In preparing bag ammunition the ignition ends are pre¬ 
pared first and quilted in special sewing machines using bronze 
needles. 

The bags are manufactured for each index of powder as 
required, as the weights of charge vary with the dififerent indexes. 
The powder is weighed out, dumped loosely in the bag and the 
lacing passed. The bag is then rolled a number of times, the 
lacing tightened and secured and the bag gauged for size, then 
placed ignition end down on a clean sheet of paper in the powder 
tank. The tanks, when marked to show the contents, are then 
ready for delivery. 









5 66 


Naval Ordnance 


Stacked Charges. 

721. There are several forms of stacking machines in use, all, 
however, working on the principle of upending the grains and 
passing them through apertures and laying them on end on a plate. 
The grains are then passed along, scooped together in one layer 
and moved over a cylinder which is covered by a brass plate. 
When the layer is in position the plate is pulled out, the layer 
drops down on the one below it and is then forced down the 
cylinder until there is space for the next layer. When the cylin¬ 
der has the required number of layers a bag is pulled over it, the 
cylinder withdrawn and the bag laced and sewed up. Plate XI 
shows a stacked charge. 

Marking of Ammunition. 

722. All ammunition is carefully marked or tagged to identify 
it. Tags are placed in the powder charge, the powder bags are 
stenciled, projectiles are painted in colors, ammunition boxes and 
powder tanks are both painted in colors and stenciled. 

These markings are self-explanatory, except the colorings used. 
By means of the markings information is given as to the caliber 
of gun for which made, weight of total charge, weights of indi¬ 
vidual fractions of charge, weight of ignition charge, index num¬ 
ber of powder, depot from which shipped, initials of weighers, 
gaugers, checkers, and inspectors, date put up, standard I. V., 
and any other information of value. 

The colors used on projectiles and boxes show the type of pro¬ 
jectile, kind of burster charge, type of fuse, weight, whether or 
not fitted with tracer, and any other necessary or valuable infor¬ 
mation. 

The details of marking are given in a Bureau of Ordnance 
pamphlet where the method and details of the information to be 
given are laid down. These instructions are changed from time 
to time as found necessary. 


Ammunition and Ammunition Stowage 


567 


PART II. 

Section I.—Ammunition Stowage and Supply. 

723. With the exception of detonators and pyrotechnic material, 
all ammunition, of whatever character, is stowed in specially con¬ 
structed stowage spaces or rooms set apart for that purpose alone. 
Ready service magazines are provided near the guns for emer¬ 
gency use. Projectiles for broadside guns may be stowed in bins 
in the compartment or passageway near the foot of the broadside 
hoists. Turrets may have projectiles stowed outside of the pro¬ 
jectile rooms either in the turret or below the turret floor. In the 
more recent designs, no turret projectile rooms are required, as 
the projectiles are stowed in the barbette (see Chapter X, 
Plate III). 

724. In the older battleships the magazines are placed in groups, 
forward and aft, connected by wing passages and ammunition 
passages, which are useful in transporting ammunition from one 
group to the other in case a turret should become disabled. In the 
recent designs of all big gun ships, the location is more compli¬ 
cated. Where there are more than four turrets the magazines are 
in three groups, and where there are four turrets they are in two 
groups, one forward and one aft, without direct communication. 

The simplest and surest solution would be to install a magazine 
and projectile room directly under the guns it would serve regard¬ 
less of caliber, with the hoists leading directly up to the guns. 
This would involve placing a line of magazines along each side of 
the ship, adjacent to machinery spaces. This solution is not 
feasible as the rooms would be too near sources of heat and also 
the space is required for other purposes. 1 his result is obtained 
for turret guns, however, as the handling of large charges and 
projectiles, obviously, must be reduced to the minimum. In addi¬ 
tion, the space below turrets is available for division into ammuni¬ 
tion spaces. 

With broadside guns, however, the magazines and projectile 
rooms are grouped forward and aft, requiring transportation of 
the less weighty charges to the base of each broadside hoist, either 
below decks or above decks. 

725. The magazine spaces are on the upper and lower platform 
decks, which places them below the protective deck for security. 


S 68 


Naval Ordnance 


They are placed inboard as a further protection in case the skin 
is pierced, to reduce the chances of an internal explosion. The 
projectiles for main battery guns for the first all big gun ships 
and a part of the powder are stored on the upper platform deck in 
ammunition rooms leading ofif the handling rooms, and the re¬ 
mainder of the powder in compartments directly below the 
handling room on the lower platform deck. In later designs 
turret projectile rooms are dispensed with as noted above. The 
ammunition for broadside guns is stowed on the lower platform 
deck, with the rooms communicating with ammunition passages or 
handling rooms in which the hoists are placed. Conveyors are 
used to transport the ammunition to the bases of the hoists. In 
certain designs it has been necessary to handle the broadside 
ammunition in two stages, bringing it up from the forward and 
after groups to the third deck and transporting it by conveyor 
to hoists which serve the individual guns. 

726. Adjacent turrets have their handling rooms connected for 
the interchange of ammunition. To get ammunition from a 
forward to an after handling room it is necessary to use the 
passages on the third deck by hoisting ammunition up special 
hatches and transporting it along the deck with overhead trolleys. 

727. Special rooms are arranged for torpedo war heads, saluting 
charges and small-arms ammunition. 

728. Plate XII shows the arrangements of ammunition spaces 
on a modern battleship. Plate XIII shows the method of stowing 
projectiles. Plate XIV shows a broadside powder tank stowage 
arrangement. 

The ammunition rooms of other ships are arranged in two 
groups forward and aft with hoist adjacent, thus requiring the 
transportation of the ammunition on deck. In general they follow 
the designs for battleships. Destroyers follow in general the 
same arrangement as is found on board larger ships. Submarines 
have special stowage arrangements due to lack of space and small 
quantities carried. 

Flooding. 

729. Ammunition rooms require special flooding, ventilating 
and lighting arrangements. 

730. The property of an explosive of resisting for a certain 
length of time, without decomposition, the action of humidity, 


CHAPTER XVI. PLATE XII. 


FORT SIDE UPPER PLATFORM 



STARBOARD SIDE LOWER PLATFORM 



AMMUNITION STOWAGE. (UPPER AND LOWER PLATFORM DECK OF A DREADNOUGHT.) 











































































































































































































































































































































jD&cA- 





S/.EMT/OAT. 


CHAPTER XVI. 


PLATE XIII. 





B£CT/0/V /FT /9-B 

12 -INCH AND 14 -INCH SHELL STOWAGE. 

















































































































































































































































































































































































































































































CHAPTER XVI 


PLATE XIV, 


T/t/re/JJecA 




5-INCH POWDER-TANK STOWAGE. 









































































































































Ammunition and Ammunition Stowage 


569 


heat and other elements which tend to cause it to decompose, is 
called its chemical stability (see paragraph 46 ). To prevent 
damage from an explosion from this loss of chemical stability, 
especially in the event of a fire, flooding arrangements are pro¬ 
vided aboard ship. In order to conform to the requirements for 
water-tight integrity, and to provide for flooding, all ammunition 
rooms are water-tight compartments. Arrangements are made for 
admitting sea water to each room or compartment where ammuni¬ 
tion is stowed. Those above the water-line have pipes leading 
from the fire main ; those below have pipes leading from sea valves. 
Where the pipe has one large opening it is called a “ flood pipe.” 
Where the pipe has many small openings on the upper side and is 
suspended across the top of the powder or projectile bin, it is 
called a “ sprinkler pipe.” In recent designs, ammunition com¬ 
partments are fitted with both types. Sprinkler pipes are also fitted 
over gun-loading positions in turrets, over powder-loading posi¬ 
tions in handling rooms, and over projectile bins when located in 
passageways. Sprinkler holes are not over j|-inch in diameter, and 
their aggregate area equals 150 per cent of the area ot the gioup 
control valve. One hole is placed over each tank or case, and if 
of insufficient size to flood the compartment in the time allowed, 
additional holes are used. When using both flood and sprinklei 
pipes sufficient water must flow to fill the compartment in 20 
minutes. Where the sprinkler pipe alone is used it must be capable 
of filling the compartment in one hour. Arrangements are made 
for sprinkling in dry dock. 

731. The flood pipe leading from a sea valve has a flood valve 
in the magazine, connected by a spindle to the berth deck to permit 
operating either in the magazine or from the deck above. The 
spindle passes through a water-tight stuffing box in the deck and 
ends in a square section in the flood-valve deck plate. A special 
wrench fitting the square head is required to operate the valve. 
This wrtnch is stowed in a locked rack on the bulkhead nearby. 
Sometimes a hinged cover plate fits over the spindle head secured 
with a padlock. The latest method is to encase the end of the 
spindle in a glass-front locked box. The keys are kept with the 
magazine keys which by naval regulations are kept in the captain s 

cabin. 


570 


Naval Ordnance 


732. The flood-valve deck, or the case, is marked with the name 
and number of the compartments it floods and an arrow indicates 
the direction in which the valve opens. In addition, specially 
shaped plates, with red ground, secured to the beam overhead, give 
the same information. 



Fig. 123 . 


733. In older ships each room is flooded by a separate valve, but 
in more recent designs the valves are arranged to flood groups 
of magazines. In this case, the control valve is located in a com¬ 
partment below the lowest water-tight deck, usually the upper 
platform deck, and is arranged so that it will flood all rooms in 
its group by operating the valve, in the handling room which the 
magazines in question serve, or from the deck above. Each room 
is fitted with a cut-off valve and a check valve, so that any one 
or more in a group may be flooded. Plate NV shows the group 
control flooding arrangements on a new ship. The valve and the 
rooms it floods are shown, and the different places where the 
valve may be operated except those on the deck above. Valve 
openings in flood pipes are fitted with caps and draincocks for 
testing purposes. 

734. As the fire main pressure would be communicated to the 
bulkheads when a room became filled, it is necessary to provide a 
relief. This is usually in the form of an exhaust ventilator of 
such diameter that the flow of water will not permit the pressure 
in the flooded room to rise above that for which they have been 
tested. 

735. Magazines are not connected to the ship’s drainage system 
direct. Ordinarily, they are drained by portable pumps, or by a 
drain to the bilge or another compartment, which is connected to 
the main or secondary drain system. 

Cooling and Ventilation. 

736. The property of imparting on firing during a greater or 
less length of time, the velocity and pressure found on acceptance 
test, is called the “ballistic stability” (see paragraph 47 ) of a 

























CHAPTER XVI. PLATE XV. 


( C.ONTROL VALVE OPERATED FROM 
A-31A, 0 32* AMD 3RD DECK 


CONTROL VALVE TO BE OPERATED 
FROM A- 3l*V AMD 3 KP DECK 


CONTROL. VALVE TO BE 
OPERATED FROM A 31A AMD 
1RO. DECK. 




m THE CASE OF 8.5 -45 T04-8 
COMPT. MOi. A-309-M, A 3I0 M 
AND A-3U M WILL BE FLOODED 
FROM THE SAME CONTROL VALVE. 


LOWER PLATFORM DECK. 


BOTE; - TORPEDO WARHEAD ROOM, A-I06 M, SHOULD BE FLOODED BY CONNECTION TO FIREMA1N 
*IVA TORPEDO ROOM A-202; THE CUT-OUT VALVE BEING LOCATED INTHE TORPEDO ROOM 
AND ARRANGED FOR OPERATING AT THE VALVE ONLY 

comp’ts of similar hatchings oh this sheet flooded bysame control VALVE. 


- COMPTS. 

LOC. VALVES 

a. COMPTS 

LOG VALVES 

C, COMPTS. 

LOC. VALVES 

D-COMPTS. 

LOC. VALVES 

A-32T-M 

A-32.8-M 
A-32I-M 

32.2. 

32 O 

3HO. DECK 
ABOVE 32C 

A-J2A--M 
A-32 5-M 
A-2IA-M 

A- 2E5-M 

322 

3I-* 

3 kp DECK 

ABOVE 320 

A-5I7-M 

A-3I8-M 

A-3'»-M 

314- 

320 

3RD DECK 
ABOVE 320 

A 309-M 

314 

310 

3RD DECK 

ABOVE 320 


GROUP CONTROL FLOODING ARRANGEMENTS . 




















































































































































572 


Naval Ordnance 


propellant powder. In order that this property be not impaired, 
arrangements are made for uniform storage conditions requiring 
either refrigeration or special ventilation. The life of a smokeless 
powder is rapidly shortened with an increase of temperature over 
90 ° F. Stabilized powders have better chemical stability than 
unstabilized powder, resisting changes due to increased tempera¬ 
ture better, lasting the same length of time in an atmosphere 20 ° F. 
higher. It has been found that a temperature of 70 ° to 8 o° F. 
is suitable for the storage of standard navy smokeless powder. 
To provide a uniform cool atmosphere in the magazines, various 
systems of refrigeration have been tried with varying success. 
However, at the present time, due to the increased stability of our 
powders, to disadvantages in refrigeration systems, and to im¬ 
proved methods of ventilation, refrigeration is no longer re¬ 
sorted to. 

The old systems were of two general types: ( 1 ) Using air 
cooled in a refrigerating box, which served both to cool the maga¬ 
zines, and ventilate them; and ( 2 ) using brine pipes in the maga¬ 
zines themselves, which necessitated an independent means of 
ventilation. 

737. The following considerations govern the installation of 
ventilation systems for magazines: 

(a) Attention to water-tight integrity of the ship. 

(b) Ventilating pipes so installed that no compartment can be 
flooded from another through the ventilating pipe. 

(c) Ventilating pipes water-tight below the lowest water-tight 
deck. 

(d) Intakes so located as to minimize the possibility of draw¬ 
ing in gas from fires in action. 

(e) Natural exhausts fitted to a fixed height above water-line. 

(f) Exhausts located inside barbettes. 

(g) Intakes fitted to prevent foreign matter entering. 

(h) Lower ends of exhausts fitted with check valves to permit 
egress of water or air, but not permit ingress of either. 

(i) Lower ends of supply ducts fitted with water-tight covers 
for sealing in action. 

(j) When ducts pass through a deck or bulkhead, to be fitted 
with a valve. 

(k) Must reduce the temperature from no° to 90 ° F. when 
the outside air is 8 o° with the usual installation. 


Ammunition and Ammunition Stowage 


573 


738. Most of the above are self-explanatory. The exhaust duct 
is fitted with a non-return flapper valve and leads up through the 
deck inside a barbette where it ends in a goose-neck covered with 
wire mesh. The air escapes then through the turret. When a 
magazine is flooded, the water escapes in the same way when the 
compartment is filled and prevents pressure being brought on the 
bulkheads. The height is fixed above the water-line by the hydro¬ 
static pressure which the compartment is designed to withstand. 
Magazines do not require ventilation in action so the blowers are 
stopped and the supply ducts sealed with hinged covers dogged 

tight- . . 

739. Magazines are insulated with cork composition in order to 
reduce to the minimum changes in temperature. The insulation 
is shown on Plate XIV. 

740. When the outside temperature is above 90 F. in day time, 
magazines may be kept cool by running the blowers only at night. 
It is advisable not to force hot air in, but allow the cool night 
air to gradually warm up during the day. In case a magazine is 
so situated that it naturally heats up to a temperature exceeding 
that of the outside air this will not hold good. 

Magazine Lighting. 

741. In the older type ships, light boxes are provided inset in 
the bulkheads, so as to throw light through round double-lens 
ports in three directions. The boxes are water-tight and open 
only from the outside of the compartment they illuminate. Each 
one contains incandescent lamps and a fitting lor a candle in case 
the lamp fails. They are arranged so that the bottom may be 
covered with water in case the candles are used. Hand electric 
storage battery lanterns have replaced candles as a secondaiy 
system of lighting. They are hung on the bulkheads on brackets. 
Later ships are fitted with bunker lights recessed in the bulkheads 
or attached to the bulkhead on the inside of the magazine. These 
special magazine fixtures have two lamps connected to separate 
feeders on the magazine circuits which are distinct from other 
circuits The control switches are removed from the paths of 
ammunition handling. They are encased in flame-proof boxes 
and assembled in groups. 


574 


Naval Ordnance 


742. Turrets are equipped with the same fixtures as magazines, 
and are also arranged with duplicate feeders. The auxiliary 
system in turrets is controlled in the turret officer’s booth. 

The auxiliary lighting system is so arranged that, when the main 
circuit fails, the auxiliary circuit will light up. 

Supply. 

743. The efficient supply of ammunition to the guns is of prime 
importance, and must be so arranged as to permit a sustained fire 
without causing a delay at the gun for lack of it, or an excess 
accumulation with the attendant danger of an explosion initiated 
by a shot from the enemy. 

The problem varies with each individual installation. The 
design is the best that can be worked out for the individual ship 
for it must be co-ordinated with other factors. The success will 
depend on the proper utilization of the equipment provided, so 
that many losses in time attributed to the equipment may be 
eliminated with the proper stationing and training of the personnel. 

744. The supply in turrets is very simple. Ammunition hoists 
for turrets are described in Chapter X. The broadside guns are 
served by chain hoists, motor driven, usually one hoist to two guns. 
The ammunition is conveyed by conveyor to the foot of the hoist 
and is delivered near the gun outside of its working circle. Plate 
XVI shows a broadside hoist without flame-proof doors. 

The bottom of this hoist is situated in a broadside handling room 
oi in a passageway. It is covered at the bottom with a flame-proof 
door. In the older types as the Connecticut class, where fore and 
aft passageways are situated below the protective deck, the am¬ 
munition is conveyed to each hoist. In the newer designs where 
fore and aft communication is impossible below the third deck, 
it is necessary to have two sets of hoists and conveyors. The 
ammunition is sent up either forward or aft to the third deck 
and then distributed by conveyors to the gun hoists. To supply a 
turret aft from forward or vice versa, the same procedure is neces¬ 
sary. Redistribution of ammunition is a slow process and would 
onlv be done in a lull in an engagement. 

745. Powder paths.—Special precautions are taken to prevent 
accidents due to flames striking powder as it is being passed along. 
To prevent the spread of flames, in case the existing arrangements 


CHAPTER XVI. 


PLATE XVI. 



r 

-T i 

u 1 

- ' p 

UH5 ji, ^ 

r 

/—POSITION OF DELIVERY TABLE 
l 1 WHEN LOWERING AMMUNITION 

GUN DECK 

• 

CARRIAGE 


































































576 


Naval Ordnance 


do not prevent this, all compartments through which powder is 
passed are protected with flame-proof scuttles. Water tanks are 
also arranged at intervals to permit wetting down a charge in 
case the sprinkling facilities are not adequate. The old type con- 



Fig. 124 . 

sisted of a swinging brass flap fitted over the opening in a door, 
and did not effect the desired result, as it left the way open when 
a powder charge was being passed from one compartment to 
another. Fig. 124 shows the latest flame-proof scuttle as installed 
on recent ships. 

























































CHAPTER XVII 


PLATE I 



BATTERY SHOWING 3", 4", and 5" GUNS ON CIRCLES, VELOCITY 
SCREENS, AND ARMOR BUTTS. 









CHAPTER XVII. 

THE PROVING GROUND. 


746 . The U. S. Naval Proving Ground is situated at Indian 
Head, Md., and comprises a tract of land of nearly 2200 acres 
on the left bank of the Potomac River, about 25 miles below Wash¬ 
ington. There is a clear range over the water of 17,000 yards. 

This is commonly known as the Upper Station. The Lower 
Station at Dahlgren, Va., is 45 miles below Indian Head on the 
right bank of the river. Its area is about 1300 acres and its water 
range extends over 100,000 yards to Tangier Shoal in Chesapeake 
Bay. By 1923 nearly all proof work will probably be done at 
Dahlgren. 

747 . The new proving ground at Dahlgren is laid out in four 
batteries with parallel lines of fire down the river, as follows: 

Broadside . 8" to i-pdr. guns. 

Main . 10" to 18" 

Butts . 12" to 18" 

Fuse and Thin Plate Butts. 8" to i-pdr. 

748 . In addition to batteries certain essential housing units are 
required for equipment: 

Physical laboratory, containing instruments, plotting room, etc. 

Bombproofs, providing shelter for ammunition and personnel. 

Shell house, for measurement and preparation of shell. 

Filling houses, for filling shells with high explosive. 

Bag house, for manufacture of bags. 

Quilting house, for sewing in ignitions. 

Assembly house, for assembling fixed ammunition. 

Magazines, for stowage of stock ammunition. 

Explosion chambers, for fragmentation work. 

Explosive sheds, for preparation of mines, etc. 

749 . All guns, gun carriages, ammunition, armor and new 
devices in naval ordnance are tested at the Proving Ground before 
being accepted for service. 

750 . The Ordnance Department at the Proving Ground is 
divided into: Gun, powder, butt, ranging, aviation and experi¬ 
mental divisions. 


579 






580 


Naval Ordnance 


751 . Proof of guns and mounts.—Every gun manufactured for 

the naval service is submitted to proof before being sent aboard 
ship. 

752 . Guns are built at private plants or at the Naval Gun 
Factory. After preliminary examination by government inspec¬ 
tors, guns are shipped to Proof Shop in Washington Navy Yard, 
where lapping out, bore searching and star gauging are done. 
Thence gun is shipped to Proving Ground. 

753 . Proof consists of five rounds: 

1. Low, from 7 to 12 tons. 

2. Service, around 16 tons for modern 45- and 50-caliber guns. 

3. Near proof, about one ton less than proof. 

4. Proof, 25 per cent overload, not exceed 20 tons. 

5. Service. 

754 . Lined guns are given an extra proof round. 

Desired pressures are obtained by using powders of well- 
known regularity kept on hand for station use. Accurate curves 
of such powders are always available. To secure proof pressure a 
faster powder (i. e., higher pressure for same weight of charge) 
is frequently necessary, due to high density of loading. 

755 . Accuracy, precision and scrupulous care are vital to good 
proof work. Laboratory methods are not lacking: every test is 
experimental in the sense that results from use of any new piece 
of ordnance are always uncertain. Thus, before proving a gun 

Bore is carefully examined. 

Chamber, rifling, and built-up parts are studied for defects. 

Breech mechanism is worked slowly. 

Ammunition is prepared with equal care: 

Temperature of powder taken. 

Weight of charge and ignition carefully checked. 

Shell and band dimensions taken with micrometer. 

Shell weighed. 

Shell seating measured. 

All data is entered on a large form sheet called the “ firing 
record.” This is copied into smooth books, which constitute a 
running log of all firing at the Proving Ground. 

Next, pressure gauges (see paragraph 802) are got ready and 
put in gun behind charge. Abnormal readings are thrown out. 
As this method is probably not accurate closer than one-half ton, 


The Proving Ground 


58i 


three gauges are always used and six for proof rounds in major- 
caliber guns. 

756 . After firing each round a thorough inspection is made of 
gun and mount for 
Damage to lands. 

Shifting of tube or hoops. 

Cracks in screw box, plug, or muzzle. 

Recoil and counter-recoil. 

Blowbacks and obturation. 

Primer vent. 

Salvo latch. 

Elevating and training gear. 

Damage or failure in any way of mount. 

757 . Common defects in guns are invisible without bore search¬ 
ing the gun. Occasionally a pressure gauge is shot out giving a 
characteristic series of deep bruises oppositely disti ibuted along 
the bore. A steel splinter or fragment may tear or roll up an 
entire land. When shells break up the damage appears to combine 
that caused by gauge and splinter, io avoid such injuries shells 
are always wiped clean and examined before filing. 

758 . Some guns are given special proof as follows: 
i2"/45 guns and above are given two 20-ton rounds. 

Relined guns are given an extra round below service pressure 

to set the liner. Essential difference between new and relined 
guns lies in the fact that repeated firing in service has set up 
stresses and states of crystallization in the old gun that prevent 
the same pressure of fit obtainable in shrinking the jacket and 

tube (or liner) together in a new gun. 

All semi-automatic guns are given ten extra service rounds of 

rapid fire to test breech mechanism. 

Type guns, i. e., guns of new design, are given a more thorough 

series of tests, velocities always taken, and shells langed. 

759 . After proof the gun is returned to the Naval Gun Factory 
at Washington, where it is stamped with the letter “ P,” and the 
initials of the officer in charge at the Proving Ground. It is 
thoroughly inspected and star gauged before issue to service. 

760 . Target, common, obsolete A. P. shell, or slugs, are usee 
in proof of gun. Provided pressures can be obtained and the 
shell’s band fits the gun, economy is the deciding t actor in the 
choice of proof projectiles. 


582 


Naval Ordnance 


761 . Mounts are generally proved at time gun is being proved. 
In case mount alone is being proved, only three rounds are fired: 
Service, proof (one ton below proof pressure for that type of 
gun), and service. 

762 . Some mounts are given special proof: 

4" twin-mount guns are fired in salvo for the last round and 
elevated 20°. 

3V50 Mark VII Mod. 2 (high angle) mount has last round 
fired at 30°. 

Turret mounts are not proved except in case of new design. 

25 per cent of all deck lugs for new ships are proved by being 
fitted in station girders during proof of guns. 

Type mounts are given extra rounds in proportion to the 
degree of change made from standard mounts. 

Slides are proved with new guns. No special rounds are fired 
unless examination of recoil record shows slide’s performance is 
unsatisfactory. Major-caliber guns are fitted with Tabor indi¬ 
cators. 

763 . Proof of powder.—An “ index ” of powder is, generally 
speaking, the largest amount of a single kind of powder that the 
capacity of the manufacturing plant is capable of blending. 
Blending houses are usually large enough to mix 125,000 pounds, 
and this number therefore represents the maximum weight of one 
index. The weights of the indices of the various sizes of powder 
are given in the Bureau of Ordnance Specifications for the Manu¬ 
facture of Powder. 

After the manufacturer’s lot is boxed and ready for shipment, 
a sample of the prescribed weight is sent to the Proving Ground 
for proof : 

764 . On the battery the following program is carried out: 

(a) Powder sample is heated for at least three days in constant 
temperature magazine until it has acquired a uniform temperature 
of 90° F. (32 0 C.). 

(b) Curve of some powder with similar characteristics is laid 
out for reference. 

(c) A warming round is fired. 

(d) A small charge of the new powder, estimated to give about 
2000 f. s., is carefully weighed, stacked (if 12" or above) and 
fired. 


The Proving Ground 


53.3 


(e) By plotting this point on the velocity-charge sheet and 
applying the “ Le Due slope ” successive rounds are selected, 
weighed, stacked and fired. (The Le Due slope is obtained from 
the Le Due formulas, which are mathematical expressions of the 
relations between gun, powder and velocity, using as arguments 
the known dimensions of each). (See paragraph 113 and Hate 
V, Chapter III.) 

(f) A new curve is fixed through the series of shots. Seivice, 
reduced and target practice charges are assigned from the points 
at which the curve cuts velocity and charge for these. 

(g) A pressure curve is plotted at the same time. 



A powder may be rejected for an irregularity of one-half of 
1 per cent of service velocity ; thus an average of 14 s. error is 
allowed for a 2800 f. s. powder. Failed powder may be redried 
or reblended for further test. 

765 . Pressures must be of fair regularity, and the pressure 

curve not too steep. . 

Assigned charges and pressures must also be within limits set 

by specifications. . 

A powder’s web-thickness, volatiles, and n.trat.on determine its 

fitness for use in any particular gun. . 

During the firing of the proof powders, a sample is taken out 
and sent to the laboratory for analysis, in order to ascertain 
whether the stability, percentage of nitrogen, residual volatiles 
and solubility are in accordance with the specifications. 

766 . Powder for current use is blended from time to time and 
stored in the proving-ground magazines. 


































584 


Naval Ordnance 


Guns of all calibers and all known indices of powder are kept 
on the station at all times for use in the proof work. 

767 . After fixing the charge, a report of the ballistic and 
chemical qualities is forwarded to the Bureau of Ordnance, upon 
which the powder is either accepted or rejected. If accepted, an 
index number is assigned and, together with the charge and 
manufacturer’s lot number, is stenciled on the boxes, and the 
index is shipped to a magazine. 

768 . Proof of shell.—The navy purchases: “Armor-piercing 
shell,” target shell, common shell, proof shot (“slugs”), high- 
capacity shell, illuminating shell, marker shell, and shrapnel. 

Armor-piercing shell are manufactured in lots of 500. None 
below 6 inches are now made. Inspection and metallurgical tests 
are made at the projectile plant. Four projectiles are selected 
from each lot, banded and capped and shipped to the Proving 
Ground for ballistic test against armor. In addition four pro¬ 
jectiles will be selected from the first lot of each caliber, capped 
and banded, three to be fired for flight and one to be burst for 
fragmentation. These projectiles must give smooth flight; must 
not break up, upset or strip their bands, or develop faults which 
would seriously afifect their value as projectiles. The dispersion 
and ranges of the projectiles fired for flight under favorable con¬ 
ditions shall not differ greatly at any range from those of standard 
projectiles already in the service; and, in all, the dispersion shall 
be such as not to afifect their value as service projectiles. Should 
the ballistic test indicate that these projectiles have developed any 
fault which will seriously afifect their value as projectiles, the 
bureau reserves the right to be furnished with three additional 
test projectiles from the lot in order to determine the fault in 
question. 

769 . The ballistic test against armor requires that two out of 
four projectiles pass through face-hardened plate and be recovered 
in effective bursting condition. This effective condition is judged 
by whether or not the cavity is exposed. Angle of plate to line 
of fire and velocity of shell are set forth in current Bureau of 
Ordnance specifications. Latitude of 40 foot-seconds in striking 
velocity is allowed the Proving Ground. Plate is selected so as 
to have its thickness equal to that of the shell’s diameter. In the 
case of 16-inch shell such plate is not always available. Velocity 
is then altered in accordance with the De Marre formula. 


The Proving Ground 


5»5 


A retest of a rejected lot may be permitted, in which three 
shells out of four must pass. 

770 . Charges for shell test are picked from curves of powder 
in current use. Corrections for temperature (about 2 foot-seconds 
for each degree F.) and for erosion are made. 

A pasteboard screen is placed in the line of fire in forward 
velocity screen to ascertain if the shell flights truly, i. e., with its 
axis tangent to line of fire, or to show if it breaks up. 

After impact the dimensions and position of impact are noted. 
The shell is recovered, inspected, and photographed. Occasionally 
heat cracks develop in the shell while it lies in the sand pile it has 
entered after leaving plate. These defects are not ordinarily held 
against the shell. 

771 . Common shell include all calibers below 7 inches, and they 
are now fired at homogeneous plates of a thickness equal to about 
one-third the caliber of the shell. The projectile must pass 
through the plate unbroken and be recovered in a condition for 
effective bursting. At present one per lot is tested against plate. 

Common shell are also fragmented and fired down the range 
according to the specifications. A shell is loaded, fused, and 
exploded in an explosion chamber. To be satisfactory, all parts 
must break up well. The shells fired down the range must not 
break up, upset, or strip their bands; and the dispersion must not 
be greater than that given by standard shell. All common shell 
tested on plate or on range will be brought to exact weight by 
blind loading. 

772 . Target shell and proof shot are fired for flight only. Both 
are of cast iron and are used for economy. The former are 
identical in design with A. P. shell; the latter are similar in weight, 
while cylindrical in shape. Three target shells of a lot are fired 
down the range in comparison with two or more of an accepted 
lot; they must give smooth flight and not sti ip then bands not 
show erratic dispersion. 

773 . Ranging is always done under the most uniform con¬ 
ditions. 

774 . Special attention is paid to accurate shell and band meas¬ 
urements, shell seating, weight of charge, position of center of 
gravity, eccentricity of shell form. Shells having special wind 
shields require an extra scrutiny just before nose enters gun; 
these shields occasionally knock loose. 


5 86 


Naval Ordnance 


775. The line of fire is established with a theodolite. Gun is 
trained and set at elevations up to about i8°, using clinometer, 
or gunner’s quadrant. Elevation of gun depends on purpose of 
ranging. If for coefficient of form or routine test of shell a 
single elevation of about 8° is sufficient. For checking range 
tables or investigating new type of shell various angles are neces¬ 
sary up to limit of screen lines. 

776. Observers with theodolites or transits are stationed at 
various points down the range to get horizontal angles of fall of 
shots. They are stationed so a good “ cut ” can be obtained. 
Observations are plotted on a special table in the physical labora¬ 
tory on which range stations are laid down to scale. Cameras 
and rakes may also be used for work involving simultaneous 
splashes. 

777. From data obtained in ranging a shell its coefficient of 
form is computed, which information is necessary in working out 
the “ range tables.” Later, as opportunity arises, various com¬ 
puted ranges of the table are checked. 

778. Meteorological conditions at time of firing are carefully 
recorded. Long-range firing is accompanied when practicable by 
exploration of the upper air strata, using aeroplanes and sounding 
balloons. The sounding balloon carries a combined barograph 
and thermograph. Angular observations from the earth’s surface 
give a fair plot of anemometric data. 

779. High-capacity shell are ranged in groups of three for each 
lot in comparison with one or more individuals of an accepted 
lot. Usually several shell from a contract are fired loaded and 
fused. 

780. Shrapnel are given flight and fragmentation test and 
ranged. New types are fired in a covered butt which permits 
recovery. 

781. Star shell are ranged and flighted for test of illuminating 
element. Other pyrotechnic projectiles, such as marker shell, 
spotting shell, etc., are ranged for coefficient of form, strength 
and stability in flight, and efficiency of element contained. 

782. Proof of armor.—Armor is proved ballistically under 
specifications by the Bureau of Ordnance. These specifications 
are periodically rewritten in order not only to keep up with the 
development of naval ordnance, but to insure that quality of pro¬ 
duction be held to highest standard possible. 


CHAPTER XVII. PLATE II. 



test plate 


ALL PLATES SHOWN 
THUS^ ARE OLD 
SCRAP ARMOR PLATES 

TIMBER 


SECTION THROUGH MODERN PLATE BUTT. 


earth nmvmvmm 
























5 88 


Naval Ordnance 


For ballistic purposes armor is divided into Class A, or face- 
hardened armor, and Class B, or rolled or forged steel plates. 

Generally speaking, Class A armor is attacked normally with 
even-caliber shell. 

Class B armor above 5 inches is tested with calibers about 
twice its thickness; below 5 inches, 12 -inch to 6 -inch guns are 
used. Angle of attack varies from g° to 33 0 from line of fire. 

Butts are ponderous structures of old armor plates and concrete 
with a sand hill behind to catch and hold the shell. Heavy oak 
timbers are wedged in as spacers between butt proper and ballistic 
plate. The problem of holding an armor plate buffeted by thou¬ 
sands of foot-tons of energy has only been solved very recently. 
Plate II shows an armor plate mounted in a butt ready for test. 
Even yet the methods are crude and cumbersome. 

Shell and charge are selected as for shell test with reference to 
velocity required. Class A plate is given two rounds and, to be 
successful, must prevent base of either shell from passing com¬ 
pletely through. Through cracks to edge of plate or to another 
impact also fails the plate. Centers of impacts must not be closer 
together than 2 \ calibers of shell used, or to edge of plate. (See 
Chapter XIV, Plate VI.) 

Class B plate must resist one impact of specified energy; and, 
to be successful, must not be pierced nor develop through cracks. 

Best modern shell are used in tests of armor. Also the inspector 
of ordnance at the steel works selects a plate from each group 
which, in his opinion, will give the poorest results. 

Cardboards and screens are used as in other firing. 

783. Proof of fuses and tracers.—A contract for fuses always 
specifies what ballistic test the finished article must stand. 

Tracer detonator fuses, major, medium and minor caliber 
ignition fuses are given the following tests : 

(a) Drop test: Fuses are fitted in shell and dropped 30-40 feet 
point or side down on a 4 -inch iron plate. Plunger must not arm 
or mark the primer cap. 

(b) Fragmentation test: Fuse must satisfactorily fragment a 
loaded shell or shells. This is done in closed chamber or against 
plate in covered butt. 

(c) Flight test: Fuses are fired in loaded shells over the range 
to test action of fuse plunger under retardation. Projectile must 
not burst or fuse blow out during flight. 


Ti-ie Proving Ground 


589 


(d) Plate test: A prescribed number of each lot of fuses are 
fired in loaded shell against thin plate ( 3 / 16 " to 4 V', depending 
on type of fuse. A given percentage must provide high-order 
detonations some distance behind plate. 

Various’other fuses, such as time fuses, marker shell fuses, anti¬ 
submarine detonating fuses, long delay action fuses, etc., aie 
given practically the same tests as above, depending on nature of 
fuse. Plate tests are, of course, omitted for time fuses and others 

not supposed to function through armor. 

784. Proof of primers.—All primers are now manufactured by 
the* Washington Navy Yard and Torpedo Station, and are proved 
under instructions issued from time to time by the Bureau of 
Ordnance. 

Chronoscope times are taken to check new design of primer, or 
when test is especially ordered. 

Primers are usually made in lots of one thousand, and five of 
each lot are sent to proof. As far as practicable primers are 
proved during current work. 

785. Bag gun combination primers are tested by firing one or 
two of a lot by percussion, the rest electrically, at service pres¬ 
sures or above. Unless the fault is clearly traceable to a cause 
outside the primer, all must fire on first attempt. Usual faults are. 

Cracking of insulation. 

Imperfect obturation. 

Cracks in stock. 

Burning or fusing of stock. 


Sticking in seat. 

Stripping of threads. 

In all cases, rejection depends upon degree of imperfection. 

786. Mark XIII (screw combination extension magazine) 
primers are tested by firing one or two of a lot electrically, the 
rest by percussion. As least two should be fired at or above service 
pressure. Mark XIV (screw percussion extension magazine) 
primers are usually fired at or above service pressure. 

Unless the cause is clearly traceable to some cause outside the 
primer, all must fire on first attempt. Usual faults are same as wit 1 

bag gun combination primers. . , 

787 When a primer misfires in percussion firing no secont 

attempt should be made, but primer removed and returned to 


590 


Naval Ordnance 


manufacturer. A primer being tested and failing electrically 
should not be fired by percussion as this may destroy any clue to its 
electric failure. 

In case of failure the primers are returned with the report to 
the Bureau of Ordnance. These reports include the approximate 
pressure, caliber of gun fired in, functioning of primers, and any 
damage to the primers or stocks. 

788. Proof of cases.—As far as practicable cases are proved 
during current work. Various numbers constitute a “ lot ” of 
cases, from ioo for 6"/40 to 1000 for 3 V 50 and smaller. From 
one to four cases from each lot are sent for proof. 

Each proof case must fire three rounds at or above service pres¬ 
sure, unless it fails on the first or second round. To pass satis¬ 
factory test, a case must be free from cracks or serious fluting; 
must permit the primer to be withdrawn with reasonable ease, 
and, after three rounds, must reload easily in the gun in which it 
was fired, and eject easily therefrom. 

If a case is otherwise satisfactory, expansion at the mouth 
. after firing, so that the projectile is no longer a tight fit, is not 
considered cause for rejection. 

789. Proof of explosives, etc.—Tests of explosive “ D,” 
TNT, rockets, bombs, mines, grenades, depth charges, etc., are 
continually going on at the Proving Ground. A general policy of 
specious thoroughness bulwarks the special schedule laid down 
by the Bureau of Ordnance for each particular kind of proof. 
With a large chemical laboratory on the station and the gun factory 
shops so close at hand broad facilities are available for every 
branch of ordnance investigation. 

790. Experimental proof work.—One division of the proof 
department spends its entire time in pursuit of information on 
existing problems, and in the development of new and better types. 
Closely allied are the experimental ammunition unit, which 
specializes in the preparation of ammunition, and the Special Board 
of Ordnance in the Navy Department, which directs its Proving 
Ground research through the experimental desk in the Bureau of 
Ordnance. 

Under the experimental division come meteorological and 
sondage work. Also most aeronautic ordnance and uses of air¬ 
plane in spotting and bombing are still largely in an experimental 
stage, so far as their connection with proof work is concerned. 


CHAPTER XVII. PLATE III. 




INSTRUMENTS USED IN ORDNANCE WORK. 











































» 



















The Proving Ground 


59 1 


791. Erosion is one of the special problems which require years 
for solution. By comparing the velocity and pressure losses in 
station guns at various points in their lives with new guns of 
similar calibers erosion curves are plotted; dispersion, types of 
rifling bands, shell forms, are other such problems. 

Measurement of Velocity and Pressures. 

MEASUREMENT OF VELOCITY. 

792. In measuring the velocity of a projectile, the time of pas¬ 
sage of the projectile between two points, a known distance apart, 
is recorded by means of a suitable instrument. The calculated 
velocity is the mean velocity between the two points and is con¬ 
sidered as the velocity midway between the points. In order that 
this may be done without material error, the two points must be 
selected at such a distance apart in the path of the projectile that 
the motion of the projectile between the points may be considered 
as uniformly varying and the path a right line. 

793. Le Boulenge chronograph (Plate III).—The instrument 
generally employed for measuring the time interval in the deter¬ 
mination of the velocity was invented by Capt. Le Boulenge, of 
the Belgian Artillery, and is called the Le Boulenge chronograph. 
It has been modified and improved by Capt. Breger, of the French 
Artillery. This instrument (see Fig. 126 ), consisting, essentially, 
of a brass column a, supporting two electromagnets b and c, is 
mounted on the triangular bedplate d, which is provided with 
levels and leveling screws. The magnet b supports the long rod e, 
called the “ chronometer,” which is enveloped when in use by a 
silvered-zinc or copper tube /, called the “ recorder.’ A nut 
above the recorder holds the recorder fixed in place on the chro¬ 
nometer rod. The magnet c, which suppoits the short rod g, 
called the “ registrar,” is mounted on a frame which permits it 
to move vertically along the standard. Fastened to the base of 
the standard is the flat spring h, which carries at the outer end 
the square knife i. The knife is held retracted or cocked by the 
trigger j, which is acted upon by the spring k. The chronometer 
e hangs so that one element of the recorder is close to the knife. 
The registrar g hangs immediately over the trigger. W hen the 
electric circuit through the registrar magnet is broken, the 
registrar falls on the trigger and releases the knife, which flies 


59 2 


Naval Ordnance 


out under the action of the spring h and nicks or indents the 
recorder. The tube e receives the registrar as it falls. Adjustable 
guides are provided to limit the swing of the two rods when first 



Fig. 126. 

suspended. The stand or table on which the instrument is 
mounted is provided with a pocket which receives the chronometer 
when it falls at the breaking of the circuit that controls its magnet. 



































The Proving Ground 


593 


A quantity of beans in the bottom of the pocket arrests the fall 
of the chronometer without-shock. 

The chronometer circuit is led through a contact piece (not 
shown) carried by the spring h and so arranged that the chronom¬ 
eter circuit cannot he closed until the knife is cocked. This 
arrangement prevents the loss of record through failure to cock 
the knife when suspending the rods before the piece is fired. 

In the use of the chronograph in measuring the velocity of a 
shot the following accessory apparatus is required: Targets, 
measuring rule, rheostats, and disjunctor. 

794 . Targets.—Two wire targets, usually spoken of as 
“ screens,” each made of continuous wire (Fig. 127 ), are erected 



in the path of the projectile. The targets form parts of electric 
circuits which include the electromagnets of the chronograph. 
Each magnet has its own target and its own circuit independent 
of the other. The circuit from the nearer or first target includes 
the chronometer magnet. 

The circuit from the second target includes the registrar mag¬ 
net. On passage of the projectile through the first target the 
circuit is broken, the chronometer magnet demagnetized, and the 
long rod, or chronometer, falls. When the projectile breaks the 
circuit through the second target, the short rod or registrar falls 
and striking the trigger, releases the knife, which, flying out, 
nicks the recorder at the point which has been brought opposite 
the knife by the fall of the chronometer. 


39 





























594 


Naval Ordnance 


The first target must always be erected at such a distance from 
the gun that it will not be afifected by the blast. For small arms it 
is placed 3 feet from the muzzle and consists of fine copper wire 
wound backwards and forwards over pins very close together. 
For cannon it is placed from 50 to 250 feet from the muzzle, de¬ 
pending upon the size of the gun. For the measurement of ordi¬ 
nary velocities the targets are usually placed 100 feet apart for 
small arms and 163 feet, or 50 meters, as is the practice at our 
proving grounds, for cannon. 

To avoid the effect of the blast from large guns, the first target 
should be placed about one-tenth of the expected velocity, in feet, 
from the muzzle. For example, when firing the 14-inch gun at a 
velocity of 2600 foot-seconds, the first target should'be about 250 
feet from the muzzle. 



The second target for small arms consists of a steel plate to 
stop the bullets, having mounted on its rear face, and insulated 
from it by the block w (Fig. 128), a contact spring s, contact 
pin p, and their binding screws. When the bullet strikes the plate 
the shock causes the end of the spring to leave the pin and thus 
breaks the circuit, which is immediately re-established by the action 
of the spring. By means of this device constant repairing of the 
target is avoided. 

795 . Measuring rule.—For measuring the height of the mark 
on recorder above the zero mark there is provided with the instru¬ 
ment a rule graduated in millimeters, and with a sliding index 
and vernier, the least reading being one-tenth of a millimeter. The 
swiveled pin at the end of the rule (Fig. 129) is inserted in the 
hole through the bob of the chronometer, and the knife-edge of 
the index is placed at the lower edge of the mark whose height 

















The Proving Ground 


595 


























596 


Naval Ordnance 


is to be measured. The height is then read from the scale. Tables 
are constructed from which can be directly read the time corre¬ 
sponding to any height in millimeters within the limits of the 
scale. The maximum time that can be measured with this chrono¬ 
graph is limited by the length of the chronometer rod and is about 
0.15 of a second. 


RHEOSTAT 



796 . The rheostat.—Both circuits are led independently 
through rheostats, by means of which the resistance in the circuits 
may be regulated and the strength of the currents through the 
two magnets equalized. 

One form of rheostat is shown in Fig. 130. The current passes 
through the contact spring a, and through a German silver wire 
wound in grooves on the wooden drum b. 

By turning the thumb nut, c, the contact spring is shifted, and 
more or less of the wire is included in the circuit. 
































































































The Proving Ground 


597 


Another form of rheostat, through which both circuits pass 
independently, is shown in Fig. 131, and this is the form used in 
our service. Each current passes through a strip of graphite, a, 
and the resistance in the circuit may be increased or diminished by 
sliding the contact piece, b, so as to include a greater or less length 
of the graphite strip in the circuit. 



Fig. 131. 



Fig. 132. 


797 The disjunctor.—Both the circuits also pass independently 
through an instrument called the “ disjunctor,” by which they may 
he broken simultaneously. The disjunctor is shown in elevatton 
and part section in Fig. .32. The two halves of the mstrument 

are exactly similar. 






































































598 


Naval Ordnance 


The two contact springs, c, weighted at their free ends, bear 
against insulated contact pins, e, supported in the same metal 
frame, d. The frame is pressed upwards against the spring catch, 
h, by two other contact springs, /. The electric circuit passes from 
one binding post through the parts f, e, c, and a to the other 
binding post. 

On the release of the spring catch, h, the frame, d, flies upward 
under the action of the springs, /, until stopped by the pin, g. At 
the sudden stoppage of the movement the weighted ends of the 
contact springs simultaneously leave the contact pins, thus break¬ 
ing both circuits momentarily. Mounted on a shaft are two 
hard-rubber cams, b, which bear against other springs, a, in the 
two circuits. On turning the cam shaft the connection between 
the parts a and c is broken, breaking both electric circuits, but not 
necessarily simultaneously. The circuits are habitually broken in 
this manner except when taking disjunction or records in firing. 

By means of the disjunctor both circuits are broken at the same 
instant. The mark made by the knife under these circumstances 
is called the disjunction mark, forming the datum point for the 
instrument. This point includes any difference in the times 
required for demagnetization of the two magnets, the time oc¬ 
cupied by the registrar in falling, and the time required for the 
knife to act. 

From the height of the disjunction mark as measured we obtain 
the corresponding time from the law of falling bodies: 



Now, when the circuits are broken by the projectile, the chro¬ 
nometer begins to fall before the registrar. The mark made by the 
knife will therefore be found above the disjunction mark. If we 
measure the height of this second mark above the zero, the corre¬ 
sponding time is the whole time that the chronometer was falling 
before the mark was made, and to obtain the time between the 
breaking of the circuit we must subtract from this time the time 
used by the instrument in making a record or the time correspond¬ 
ing to the disjunction. Let h x and h 2 represent the heights of the 
disjunction and record marks, respectively, t x and t 2 the corre¬ 
sponding times. Let t be the time between the breaking of the 
screens; then, 

t=t 2 -t l = ( 2 h 2 /g)i-(2 K/g)l. 


The Proving Ground 


599 


It will be seen by the equation that the difference of times, and not 
the difference of heights, must be taken. 

798 . Fixed disjunction.—For the velocity at the middle point 
between targets we have, representing by s the distance between 
the targets, 

v—s/t. 

Substituting for t its value, we have 


{2h 2 /g)l-(2h x /g)l‘ 

From this equation we see that if the value of .s' and of (2h 1 /g)K 
the disjunction, he fixed, the values of v can he calculated for all 
values of h 2 within the limits of practice and tabulated. This has 
been done for the values: s=ioo feet and (2/q/g) i = o.i5 seconds. 
This value of (2/q/g)* is called the fixed disjunction. If such a 
table is not at hand, the fixed value of the disjunction avoids the 
labor of calculating (2/q/g)^ for each shot, as in this case we have 

t = t 2 — o.is sec.= (2/io/g)- — o. 1 5 * 

In ordinary practice it is better to take the disjunction at each shot 
and to keep the disjunction mark near the disjunction circle, but 
not necessarily on it. The times corresponding to the heights of 
the disjunction and record marks are both read from the table, and 
with the difference of these times the velocity is taken from another 
table. 

The velocity obtained is that at a point midway between the two 
screens. A correction, found by the methods of exterior ballistics, 
is applied to reduce this to the muzzle of the gun whence it becomes 
the initial velocity. For practical use curves are computed from 
which the correction is picked off. 

The velocity obtained is, of course, that half way between the 
screens, and to obtain the actual muzzle velocity of the gun, this 
must be reduced to the muzzle by exterior ballistic formulas. (See 
Art. 108, Alger’s Exterior Ballistics, 1915O 

C = ; S = C (S V2 - S V1 ) ; whence S V1 = S V2 -^. 

Where V., = velocity midway between the screens, l 1 = initial 
velocity, 5 = distance from the muzzle to point half way between 
the screens, d = diameter of shell, w = weight of shell, ( = ballistic 



DOO 


Naval Ordnance 


coefficient uncorrected for atmospheric conditions, and S V2 and 
S Vl are found in Table I of the Ballistic Tables, 1914. 

At the Proving Grounds curves have been calculated from which 
we pick off for each caliber the quantity to add to the measured 
velocity to give the initial velocity. 

Example .—In the Naval Academy pistol gallery there are 
screens 67 feet apart, the first being 6 feet from the muzzle. The 
measured velocity being 772 feet, find the initial velocity. In this 
case F 2 = 772, 5 = 39.5, C=.18865 (given in description of the 
pistol). 

■S' 39-5 .log 1.59660 

C .18865 log.9.27566.colog 0.72434 

log 2.32094. . 209.38 

16248.40 


S V1 = 16039.02 
Vi= 779-6 

799 . Adjustments and use of the chronograph.—The instru¬ 
ment must be properly mounted on a stand at such a distance from 
the gun that it will not be affected by shock of discharge. The 
electrical connections with the batteries and targets, through the 
rheostats, r, and disjunctor, d, are made as shown in Fig. 133. 

To adjust the instrument, first level it by the leveling screws, 
cock the knife, and suspend the chronometer rod enveloped by the 
recorder from its magnet. See that the recorder hangs close to 
the knife and that no part of the base of the rod touches any part 
of the instrument. The guides must be close to, but not touching 
the bob of the chronometer. Release the trigger, and the knife 
will then mark the recorder near the bottom. This mark is the 
zero from which all heights are measured, and the knife-edge on 
the measuring-rule index must be so adjusted that the zero of the 
vernier shall coincide with the zero of the scale when the knife-edge 
is in the mark. The adjustment of the knife is made as follows: 
Place the sliding index so that the zero of the vernier is at the 
zero of the scale on the rule. Clamp the index and apply the rule 
to the chronometer. Loosen the screws that hold the knife and 
adjust the knife-edge to turn the recorder around the chronometer 
rod. The knife-edge will scribe a circle on the recorder, and the 
mark made at the disjunction should fall on or near this circle. 






The Proving Ground 


601 


To regulate the strength of the magnets each of the rods is pro¬ 
vided with a tubular weight, one-tenth that of the rod. Place 
the proper weight on each rod and suspend the rods from their 
magnets. Increase the resistance in each circuit by slowly moving 
the contact piece of the rheostat until the rod falls. Remove the 
weights from the rods and again suspend the rods. Take the 
disjunction. If the bottom of the mark made by the knife does 
not lie on or near the circle previously scribed on the recorder, raise 
or lower the registrar magnet until coincidence is nearly obtained. 



Test the disjunctor by shifting the two circuits. The height of 
disjunction should remain the same. Test the circuits by suspend¬ 
ing the rods and causing the circuits to be broken successively at 
the two targets. Note that the proper rod falls as each circuit is 

broken. 

Always suspend the chronometer rod with the same side of the 
bob to the front—to do this it is usual to have the number on the 
bob toward you—and always, before suspending it, press the 
recorder down hard against the bob. After each record turn the 
recorder slightly on the rod to present a new element to the knife. 





















































602 


Naval Ordnance 


Circuits should always be broken at the disjunctor when the rods 
are not actually suspended, and the rods should be allowed to 
remain suspended as short a time as possible. 

800 . Measurement of very small intervals of time.—For the 
measurement of very small time intervals the registrar magnet is 
raised to near the standard and placed in the circuit with the first 
target. The chronometer magnet is put in the circuit with the 
second target. Under this arrangement the disjunction mark will 
be made near the top of the recorder and the record mark under 
the disjunction. The interval of time is obtained by subtracting the 
time corresponding to the height of the record mark from the 
time of disjunction. The object of this arrangement is to obtain 
the record when the chronometer has acquired a considerable 
velocity of fall, so that the scale of time will be extended, and 
small errors of reading will not produce large errors in time. 

For velocity work at the Naval Proving Ground three 
Le Boulenge chronographs are used. A separate circuit and 
screens are provided for each instrument. These triple screens 
are placed a few inches apart, the first of one set being exactly 
50 meters from the first of the second set. The use of these three 
chronographs permits the selection of the most probable results in 
case the results vary. The results seldom dififer, however. 

801 . Schultz chronoscope (see Plate III and Fig. 134).—The 
Le Boulenge chronograph measures a single time interval only. 
Where more exact results must be obtained in time measurements, 
such as velocities of recoil and counter-recoil, the firing interval, 
or in any case where several consecutive intervals must be mea¬ 
sured, an instrument called the Schultz chronoscope is used. 

This instrument consists, essentially, of a nickel-plated cylinder, 
a, revolving by means of a falling weight, the speed of rotation 
being rendered constant by means of a fan in gear with the 
mechanism. A stylus, //, is fastened to one prong of an electrically 
sustained tuning fork, b. The breaking of an electric circuit 
is the means employed to mark successive intervals of the measure¬ 
ment; the break causing a spark to leap across from a point near 
the stylus on the tuning fork to the metal cylinder, the latter having- 
been coated lightly with lampblack just before the measurement is 
to be made. As the cylinder revolves and the tuning fork vibrates 


The Proving Ground 


603 


a wavy line is traced on its surface, and each spark is marked on 
the line by a small bright dot whenever the current is broken. 

There is another method of registration in which the circuits 
that are broken pass through the Marcel Drepez registers, e, 
Fig- 135- When the circuit is broken the magnet, e, Fig. 135, is 
demagnetized and the spring, g, rotates the armature, f, and its 
attached stylus or quill, h, thus making a bend or ofifset in the trace 
of the quill on the cylinder. The spark type of chronoscope wherein 
a splatter or bright dot on the lampblackened cylinder is made by 



a spark instead of the ofifset by magnet, is used at the Naval Prov¬ 
ing Ground, for the reasons that it is as accurate, more easily kept 

in repair, and is much easier to use. 

The speed of the tuning-fork vibrations is nearly constant, being 
equal to about 250 per second. The distance between two sparks 
in terms of the vibrations would then measure 0.004 second. By 
means of a magnifying glass and micrometer the wave length may 
be divided quite accurately into 100 parts, thus permitting the 

determination of the time intervals of • 0Q ^ (,t " a second. 





























































604 


Naval Ordnance 


MEASUREMENT OF PRESSURES. 


802 . Gauges.—Pressures in cannon are directly measured by 
means of the navy pressure gauge (Figs. 136 and 137, and Plate 
III). In a steel cylinder or housing is assembled a steel plunger 
and a copper cylinder or disk. The cylinder is closed by a screw 
cap, the joint being made tight by a copper washer. 

A small copper obturating cap prevents the entrance of gas past 
the plunger, and the copper washer performs the same office at the 
joint between the cylinder and the screw cap. 



■<5 area Pressure Qauce. 

Scale 

Fig. 136. 

Gauges are placed in the gun behind the powder charge, or may 
be, in addition, inserted in sockets in the mushroom. Three gauges 
are also used. Those in the mushroom are generally used only in 
proving-ground work. When the gun is fired the pressure of 
the powder gases is exerted against the end of the plunger, and 
the copper disk is compressed. The compression is manifestly 
due to the maximum pressure exerted in the gun. The length of 
the disk is measured both before and after firing by a micrometer 
gauge, the compression due to pressure thus being determined. 
With this compression the pressure per square inch that produced 




























The Proving Ground 


605 


it is read at once from the compression curve furnished with each 
lot of disks. 

803 . The compression curve.—The copper disks are cut in a 
given length from rods very uniformly rolled and carefully an¬ 
nealed. The compression of the disks under different loads is 
determined in a static-pressure machine. It is assumed that the 
compression obtained in firing is due to a load on the plunger of 
the pressure gauge equal to the load that produced the same com¬ 
pression in the static machine. The pressure per square inch in 



Jo area Pressure Cauce 

Scale 

Fig. 137. 

the gun may therefore be obtained by dividing the static load that 
corresponds to the observed compression by the area of the 
plunger in the pressure gauges. Knowing the area of the plunger 
used, the table of compressions and corresponding pressures per 
square inch is readily constructed from the results obtained in the 

machine. . . 

The area of the plunger for large caliber gauges is one-sixth of 

a square inch (Fig. 136). The plunger for the 6-pounder and 
other minor caliber gauges has an area of one-thirtieth of a square 

inch (Fig. 137 )- 




































6 o6 


Naval Ordnance 


804 . Initial compression.—When the pressure in the gun is 
high the compression of the copper is considerable, and the plunger 
acquires an appreciable velocity during the compression. The 
energy of the plunger due to this velocity adds to the compression 
that would result from the pressure alone, and consequently the 
measured compression is greater than the compression that corre¬ 
sponds to the true pressure. The energy of the plunger may be 
reduced either by reducing its weight or by limiting its travel and 
hence its velocity. The plunger is made as light as possible con¬ 
sistent with the duty it has to perform. To limit its travel the 
copper cylinders are initially compressed before using, by a load 
corresponding to a pressure somewhat less than that expected in 
the gun. Further compression of the copper will not occur until 
the load applied in the gun is close to that used in the initial 
compression. 

The general practice is to give all the one-thirtieth area disks an 
initial pressure of 4 tons and all the one-sixth area disks an initial 
pressure of 9 tons per square inch. 

805 . The velocimeter measures the velocity of recoil of a gun, 
and is used in connection with a chronoscope. Its principal part 
is a drum rotated by a string made fast to the gun. Each two 
inches of recoil, by turning the drum composed of insulated seg¬ 
ments, makes and breaks an electric circuit to the chronoscope. 
A strong spiral spring takes in the slack on the counter-recoil and 
keeps a good tension on the line, so that the drum moves according 
to the recoil of the gun at all times. On the rotating smoked drum 
of the chronoscope in the laboratory, each two inches of recoil, 
then, is marked by a spark formed by an interruption in the electric 
circuit as the segments of the drum are passed over. The number 
of vibrations of the tuning-fork on the chronoscope per second 
being known, by counting these vibrations between the successive 
sparks on the drum the velocity for every two inches of recoil 
is known. 

Guns do not recoil as rapidly as might be imagined. Twenty 
feet per second, or 12 knots per hour, is a good maximum value. 
Counter-recoil velocities are about one-eighth of the value of recoil 
velocities. By studying the curve of recoil velocities in connection 
with recoil-cylinder indicator cards, abnormal stresses in the mount 
may be detected and avoided in design. 

806 . Aberdeen chronograph.—In this instrument the eletrical 
impulse recording the passage of the projectile through the screens 



The Proving Ground 


607 


is a “ make ” in the circuit, instead of a “ break ” as in the 
Boulenge. The mechanism consists of a shallow aluminum cylin¬ 
drical drum driven by a series-wound ball-bearing motor, at a 
constant speed of 25 revolutions per second, the speed being con¬ 
trolled by a governor acting through resistances in the full line 
voltage. The screens consist of two metal plates (tin or tinfoil) 
separated by an insulating sheet of paraffined paper. The circuit 
leads from one plate of the screen to the spark point held in an 
insulated block 0.5 mm. from the inner periphery of the drum 
and from the drum through a condenser back to the other plate. 
A strip of special paraffined paper is placed in the drum and held 
by centrifugal force against its inner periphery. When the 
projectile passes through the screen it completes the circuit, caus¬ 
ing a spark to jump across from the spark point to the drum, 
perforating the recording paper. The spark points for each screen 
are vertically in line, hence the distance between marks on the 
paper, knowing the screen distance and speed of motor, represents 
the time interval between screens from which the velocity is 
determined. The instrument can be calibrated by means of a ball 
drop, i. e., measuring the known time interval taken by a ball 
dropped from a given height. 

807 . Oscillograph.—This instrument is also used at the Proving 
Ground for measuring time intervals. It consists of a finely ad¬ 
justed galvanometer, with exceedingly small period of free vibra¬ 
tion, the movement of which is recorded by means of a beam of 
light on a moving film. Time is recorded on the same film, and 
through the same means, by a carefully calibrated tuning fork, 
actuated by an electrical impuse. d he galvanometer loop is con¬ 
nected to separate circuits. 

These circuits are connected (when used in velocity determina¬ 
tions) at various points of the projectiles travel, theie being no 
current flowing except when the projectile passes that point. \Vhen 
this occurs a momentary circuit is set up which acts upon a sensitive 
galvanometer in the oscillograph. These galvanometers have small 
mirrors, which ordinarily remain in a fixed position, throwing a 
steady beam of light on the film, but are sharply deflected when 
the circuit is completed, with resultant sharp offsets at the points 
of the projectile’s passage. The distance between these points, 
referred to the record of the tuning-fork vibrations, give the time 
interval between successive passages and hence the velocity of the 

projectile. 


6 oS 


Naval Ordnance 


808 . The gunner’s quadrant consists of a flat base with a 
pivoted arm carrying a spirit level. The arm is set at the reading 
corresponding to the desired elevation, the quadrant is put on the 
gun, and the gun is elevated until the bubble centers. It is then 
at the desired elevation. (See Plate III.) 

The Vickers gun clinometer is a more accurate instrument. 
Hie level arm is adjusted to the degree next below the elevation 
desired. By turning a screw handle, a needle arm on a large arc 
graduated to minutes is worked so that the setting of the instru¬ 
ment to degrees and minutes of elevation is done more quickly 
and more accurately than with the simple type of gunner’s quad¬ 
rant. 

Droop may be expressed as the angle that the final tangent of 
the curved bore makes with the axis of the gun at the breech. To 
measure the inclination of the muzzle, a muzzle rest with two 
cylindrical disks or bearing surfaces is fitted snugly into the muzzle 
of the gun. On the central shaft of this device is placed a striding 
clinometer, lying parallel to the center line of the gun, which is 
leveled crosswise and also fore and aft with reference to the gun, 
by set-screws. In using this clinometer it is read, then reversed, 
end for end, and read again. Were the instrument perfect, the 
readings should agree. This is not generally the case, so the 
average of the two readings is taken to eliminate error. At the 
same time (the gun being approximately level) the elevation at 
the breech is taken with the Vickers clinometer (read both ways 
and averaged for the same reason). The difference between the 
elevation at the muzzle and at the breech is the droop. This should 
be only . few minutes of arc, even in the largest guns. (Plate III.) 

The Tabor indicator is similar in all respects to those used 
on a steam engine, except that the piston area is square inch 
instead of \ square inch. This is used to get pressures of the 
liquid in the recoil cylinder. It is screwed in a threaded plug¬ 
hole in the recoil cylinder, and the string is atached to the gun 
or to the yoke. When the gun is fired, a card is made showing 
the pressure corresponding to any amount of recoil. These pres¬ 
sures run from 2000 to 3000 pounds for modern guns, and the 
general appearance of the curve—the presence of “ peaks,” etc.— 
shows whether or not the recoil system is behaving normally. 
(Plate III.) 


CHAPTER XVIII. 

AIRCRAFT, ANTI-AIRCRAFT, AND FIELD GUNS. 

Aircraft Guns. 

809 . Guns for use in aircraft must be light and easily manipu¬ 
lated, and must have little or no recoil, since the structure of air¬ 
planes will not allow of any heavy shocks due to the discharge of 
guns mounted in them. The usual equipment carried by fighting 
planes consists of one or more machine guns, the latter being 
light, automatic in action, easily trained, and capable of the great¬ 
est rapidity of fire. Certain classes of aircraft carry other types 
of guns, firing a larger projectile and possessing greater destruc¬ 
tive power. These range from one-pounder guns to six- and 
nme-pounder guns, the two latter being of a special type known as 
tion-recoil guns. 

810 . The ordinary combat plane used by land forces carries 
only machine gun equipment, since it is used only in attacking 
other aircraft or exposed bodies of troops. Special mountings 
enable the gun to be quickly trained in any direction. For airplanes 
having a propeller at the forward end of the fuselage, a control 
gear is provided to synchronize the gun fire with the propeller, so 
that the gun may be fired directly through the plane of rotation ot 
the blades without danger of striking them. 1 his enables the 
machine gun operator to keep up a steady fire while flying or diving 
directly at the enemy. Tracer bullets are used, to assist him in 
bringing his shots on the target. 

Instead of firing through the plane of rotation of the blades, 
shooting dead ahead is sometimes attained by enclosing the gun 
in the crank case and firing through the hub of the piopeller. 
Obviously such a gun can be used only when the airplane is headed 
toward the enemy. 

811 . In the case of seaplanes, one important object is the 
destruction of enemy submarines. With this end in view, such 
aircraft are fitted to carry bombs, or else are armed with guns of a 
caliber sufficient to penetrate the steel hull of the submarine. 

Plate 1 shows a six-pounder non-recoil gun such as is mounted 
in U. S. Naval airplanes. It will be seen to be a double-ended gun, 

6oq 


40 


CHAPTER XVIII. 


PLATE l 



6-PDR. NON-RECOIL GUN WITH LEWIS MACHINE GUN 

POINTER. 


CHAPTER XVIII. PLATE II. 



LEWIS CUN- 

BOWDEN WIRE- 

. BREECH THREADS- 

GUN OPERATING HANDLE 
SHOULDER BAR 


YOKE 

BOWDEN WIRE CLAMP 


FORWARD TRIGGER 

(Ror lewis gun) 


TRIGGER 
(RDR DAVIS GUN) 


Fig. i.—Rear Barrel Unscrewed and Pulled to the Rear Ready 
to Rotate to the Right. Note Also General Assembly. 



Fig. 2._Breech Open. Note Position of Gun-Operating Handle 

and Cocking Lever. 

6-PDR NON-RECOIL GUN SHOWING DETAIL OF BREECH AND 
LEWIS MACHINE GUN POINTER. 








6 l2 


Naval Ordnance 


in which the recoiling force of the forward barrel is counter¬ 
balanced by that of the rear barrel, from which a dummy charge 
is fired simultaneously with the projectile, this dummy charge con¬ 
sisting of fine shot. There is but one powder chamber; half of the 
powder may be considered as propelling the forward projectile, 
and the other half as propelling the dummy charge. The result is 
that one explosive force counteracts the other, and practically no 
shock of recoil is transmitted to the mount. The latter can there¬ 
fore be made comparatively light, as is necessary in aircraft to 
eliminate weight, and in addition, little or no force is transmitted 
to the gun platform. Plate I shows not only the six-pounder gun 
and mount, but a superposed Lewis machine gun as well, and also 
the method of mounting and operating the gun in the cockpit of an 
airplane. 

812 . The non-recoil gun consists essentially of three parts: 

the forzvard barrel . the rear barrel, and the group of zvorking parts. 
The latter includes the operating handle, the rotating shaft . and the 
firing mechanism and attachments. 

The barrels are each formed of a single forging, the forward 
one being chambered at its breech end to take the special type of 
ammunition provided for these guns. (See Art. 675, Fig. 117. 
Chap. XVI.) Beyond the chamber, this barrel is rifled as in the 
case of other guns. Shrunk over its breech end is the breech band, 
on the inside of which are cut the usual type of interrupted screw 
threads. The rear barrel is not rifled, but is smooth-bored for its 
whole length. The breech end of the rear barrel (which in this 
case is its forward end) is threaded on the outside to conform with 
the threads on the inside of the breech band on the forward barrel. 

Plate II furnishes a good idea of the parts of the gun, together 
with their operation in loading and firing. Fig. 1 shows the breech 
unlocked and the rear barrel drawn to the rear, ready for rotating 
to the open position as shown in Fig. 2. These operations are all 
performed by the gun “ operating handle." which is secured to 
the rear barrel and slides in a bayonet joint slot in the “ handle 
guide band.” As is apparent from the type of screw thread used, 
about an eighth of a turn is sufficient to unlock the breech. This 
is accomplished by moving the operating handle to the right along 
its slot, after which it is drawn to the rear, thus withdrawing the 
threaded portion of the rear barrel from the screw box. In the 
next motion the rear barrel is rotated to the right, around the 


Aircraft, Anti-Aircraft, Field Guns 


613 


rotating shaft,” until it rests on a small projection from the 
breech band of the forward barrel, in the position shown in 
Plate II, Fig. 2. 

813 . The rotating shaft extends underneath the gun (see 
Plates I and II) and serves as a bridge between the forward and 
the rear barrels. It is rigidly secured to the two guide bands sur¬ 
rounding the rear barrel, but is free to turn in its bearings in the 
breech band and the trunnion band on the forward barrel, thus 
providing a means for rotating the rear barrel to one side when 
loading the gun. 

814 . The pistol grip, the trigger, the firing rod and springs, 
and the cocking cam are all carried by the rotating shaft. Fig. 138 


O 




*WC COCXI^C 3*W**a 


I fl] 

Up 



-TRUNNION 

BAND 


BAND 


FlG . 138.— Mechanical Details of Firing Mechanism and Attachments. 

shows the arrangement of these attachments, together with the 
firing levers and the firing mechanism body, which latter contains 
the sear, the plunger, the firing spring, and the firing pm. 

The rotating shaft also carries an extractor cam, not shown m 
Fio- 1 which actuates the extractor and withdraws the shell on 

opening the breech. 

815 . Operation.— The mechanical details of the gun can prob¬ 
ably be better understood by a description of its operation during 


loading and firing. 







































































































614 


Naval Ordnance 


Consider the gun as having just been fired : 

To open the breech, the operating handle is raised slightly 
upward and rotated to the right about an eighth of a turn. This 
turns the rear barrel about its own axis as a center, and unlocks 
the breech bayonet joint. The handle is then pulled straight to the 
rear, thus sliding the rear barrel clear of the forward barrel. The 
rear barrel is then rotated about the rotating shaft as a center, 
leaving the breech clear. 

Extracting the empty shell. —The turning of the rotating shaft 
about its center also turns the extractor cam, and forces the 
extractor about a quarter of an inch to the rear. This serves to 
loosen the empty case, after which it can be removed by hand. 

Cocking the tiring mechanism. —Rotating the shaft about its 
center as an axis also rotates the cocking cam, the motion of which 
is transmitted through the cocking rod to the cocking lever at 
the top of the firing-mechanism body. The cocking lever lifts the 
firing-pin plunger and compresses the firing-pin spring. When 
the plunger is raised above the end of the firing sear, the latter is 
pressed forward by the firing-rod springs (acting through the 
firing levers), and holds the firing pin and plunger in the cocked 
position. At this point the safety scar, shown in Fig. 138, is pushed 
to the right with the thumb, thus locking the firing mechanism in 
the cocked position. 

Loading. —The gun is then loaded, care being taken that the 
“ locating boss ” on the end of the cartridge case fits into the 
locating groove in the breech band. 

To close the breech, the operations in opening are reversed. The 
rear barrel is rotated to the left about the rotating shaft, and is 
then slid forward into the screw box. The next movement rotates 
it to the left about its own center as an axis, and locks the breech. 

Firing action. —The safety sear is pushed to the left, and the 
trigger is then pulled. The trigger being pivoted near the center, 
a pull to the rear at the lower end presses the upper end forward, 
moving the firing rod forward and compressing the firing-roi 
springs. The forward motion of the firing rod carries forward 
also the lower ends of the firing levers. The latter being pivoted 
near tbe upper end by the firing-lever bolt, this forward motion of 
the lower end causes the upper end to move to the rear, withdraw¬ 
ing the sear and releasing the firing-pin plunger. Thereupon the 


Aircraft, Anti-Aircraft, Field Guns 615 

firing pin is driven downward by the firing-pin spring, striking the 
primer and firing the gun. 

816 . Machine gun pointer for non-recoil guns.—Owing to the 
difficulty of aiming a single-shot gun from a moving airplane, and 
making the proper allowance for speed of the plane, etc., a machine 
gun, as shown in Plates I and II, is mounted on the non-recoil gun 
to act as a pointer. - 

Suppose the airplane is firing at a target in the water. By ob¬ 
serving the splash of the machine-gun bullets, proper correction of 
the aim can he made, and the larger gun can then be fired as the 
line of small splashes comes on the target. Both triggers are in 
close proximity, so that either or both can be pressed without 
changing the position of the hand. 

It will be noted that the machine gun can be set at a different 
angle of elevation from that of the non-recoil gun. This provision 
is imperative, due to difference in the trajectories of the two kinds 
of projectiles, which makes necessary a certain super-elevation of 
the machine gun over the larger gun. Theoretically, this super¬ 
elevation, it has been determined, depends on two factors; first, 
the "ground speed” of the airplane, and secondly, the angle at 
which the non-recoil gun is fired. Tables have been made out 
showing the angles of super-elevation for different ground speeds 
and angles of fire. Having determined the angle at which the 
non-recoil gun is to he fired, and having ascertained or estimated 
as closely as possible the ground speed ot the airplane, the machine 
gun is set to the proper angle of super-elevation. \\ hen the target 
is sighted, the plane is flown toward it. As soon as the target 
appears on the line of sight of the non-recoil gun, the gunner 
opens fire with the machine gun and observes the location of the 
splashes. Due to the motion of the airplane these splashes will 
appear as a line, and the gunner trains both guns so that the line 
of splashes will cross the target. The instant a splash appears 
on or close to the target he fires the larger gun. 

In practice, the method of calculating the angle of super¬ 
elevation of the machine gun described above is not adhered to. 
Instead, the angle of fire of the non-recoil gun is taken as constant; 
the designed " air speed ” of the plane is used ; and the correspond¬ 
ing angle of super-elevation is permanently set before the gun is 
mounted in the airplane. 


CHAPTER XVIII. PLATE III 



Fig. i.—3-Inch 50-Caliber Anti-Aircraft Gun and Mount. 


CHAPTER XVIII. PLATE III 



41 





6 i8 


Naval Ordnance 


Anti-Aircraft Guns. 

817 . Guns to be used against aircraft must be capable of very 
high angles of elevation. The different types used in the navy, 
for instance, have angles of elevation varying from 75 0 to 90°. 
They must also have as great an arc of train as possible. For 
this reason, coupled with their extreme elevation, they are located 
at favorable points on the upper decks, on platforms on the cranes, 
or on top of the high turrets aft, where they are clear of the blast 
of turret guns. 

Certain other features are striven for in the design of anti- 
aircraft guns. They include (1) ease and rapidity of elevating and 
training, (2) rapidity of loading and firing, (3) high muzzle 
velocity, and (4) caliber large enough to produce a good-sized 
shrapnel or high-explosive burst in the air. Obviously these fea¬ 
tures cannot all be attained in one gun, as some of them are 
diametrically opposed to each other. It requires a compromise, 
which in our navy has resulted in the adoption of a 3-inch 50-caliber 
semi-automatic gun, with a muzzle velocity of 2700 f. s., as the 
type of gun for the anti-aircraft battery of battleships and battle 
cruisers. 

818 . Plate III shows the 3-inch 50-caliber anti-aircraft gun and 
mount. As will be noted, the trunnion height is considerable— 
about 66 inches—and the mount is cut away at the rear to allow 
for 90° extreme elevation. Located on the upper deck, the gun 
is capable of training through 360° and. except over small arcs 
where the masts and stacks may interfere, it can be fired at all 
angles of train. 

The gun proper consists of four parts, viz., the tube, the jacket, 
the breech housing and the locking ring. The jacket, which is 
shrunk over the tube, extends only part way to the muzzle. Over 
its forward end, and covering the joint between it and the tube, 
is screwed the small C-i locking ring. The breech end of the 
jacket is threaded on the outside to receive the breech housing, 
which is screwed and shrunk over the breech of the gun, and is 
slotted to receive the breech block. The gun is fitted to use fixed 
ammunition only, and is rifled with rib rifling, increasing twist. 

The breech mechanism is of the sliding-wedge type, and is semi¬ 
automatic in action. (See Art. 4S4 and Chapter XI, Plate V.) 


Aircraft, Anti-Aircraft, Field Guns 619 

The mount. I lie various details of the mount are quite clearly 
shown in Plate III. It will be seen that the carriage, which forms 
the greater part of the mount, rests over a low, cylindrical stand 
that is bolted to a foundation plate 111 the deck. 1 he actual bearing 
surface on which the weight of the carriage and gun is taken is 
a ball-race, designed to reduce friction to a minimum. Extending 
around the upper part of the stand, and rigidly secured to it, is 
the training rack. Neither the rack nor the ball-race is visible, 
because they are obscured by the overhang of the carriage. A 
training pinion, meshing with the training rack, is connected by a 
suitable shaft and gearing with the trainer’s two-hand drive 
shown at the right of the gun. 

On the left-hand side of the carriage is the pointer’s two-hand 
drive, which actuates a pinion meshing with the elevating arc 
shown in Fig. 2. The right handle of this drive gear is fitted as a 
firing handle. It is operated by a quick turn of the pointer’s wrist, 
which throws the handle over to one side and then back to the 
normal position again. 

At the top of the carriage are the trunnion seats in which the 
trunnions rest. The latter form part of the slide through which 
the gun slides on recoil and counter-recoil. 

The recoil cylinder is located above the gun instead of under¬ 
neath, in order to allow for greater angle of elevation. It contains, 
besides the recoil piston and liquid, the counter-recoil springs for 
forcing the gun back again to battery. The piston rod, it will be 
seen, is secured to a lug on top of the breech housing. 

Prismatic telescopic sights are provided for this gun, so that 
the pointer's position at the telescopes will be comfortable even 
when the gun is at a high angle of elevation. The sights are 
carried on a sight yoke that pivots on the slide just forward of the 
recoil cylinder bonnet. The sight bar extending to the rear, the 
deflection arc and deflection drum, the graduated sword and the 
range drum, together with the knurled heads for setting range and 
deflection, are all shown with sufficient clearness in Plate III to be 
readily understood. 

Fig. 1 shows a gun rigged with dotter gear for pointer drill. 
Fig. 2 shows the flexible metal voice tube by which ranges and 
battle orders are transmitted to the gun. This tube is coupled to 
a brass voice tube extending through the base of the mount to the 


620 


Naval Ordnance 


deck below. Fig. 2 also shows the wiring for sight lighting in case 
of firing at night. 

Ammunition.—The ammunition used with the 3-inch 50-caliber 
anti-aircraft gun is of two kinds : 

1. Shrapnel, for defence against aircraft. 

2. Non-ricocheting loaded shell for defence against submarines. 

Obviously the latter type of shell has nothing to do with aircraft. 

The guns, however, from their favorable location and the readiness 
with which they can be handled, were found to be valuable anti- 

819 . Other anti-aircraft guns.—The anti-aircraft gun just 
described is not the only one in use in the navy. There is a 3-inch 
23-caliber gun of lower muzzle velocity for mounting on de¬ 
stroyers, sub-chasers, and certain other types of vessels. In 
addition, a one-pounder automatic gun has been used to a rather 
limited extent. Still other types have been designed and may be 
submarine weapons, and in consequence were provided with the 
necessary ammunition for this purpose. 

put in service, but the 3-inch 50-caliber gun is considered repre¬ 
sentative of the class, and a knowledge of it will give a fair idea 
of all other anti-aircraft guns. 

Field Guns. 

820 . The field guns carried by U. S. ships for operations on 
shore consist of machine guns and 3 -inch held pieces. 

821 . Machine guns are automatic rifles, firing the same am¬ 
munition as the .30 caliber service rifle. The various types in 
existence are provided with the necessary mechanism for loading 
a live cartridge into the barrel, firing it, automatically ejecting the 
empty case and loading in another cartridge, and continuing the 
cycle so long as ammunition is fed to the gun and the trigger held 
to the rear. 

The energy for operating the mechanism is obtained in some 
machine guns from the recoil of the gun. In other types, a portion 
of the powder gases that propel the bullet is utilized for this pur¬ 
pose. Such guns have a small gas port near the muzzle end of the 
barrel, communicating with a gas chamber underneath. In this 
chamber is a piston on which the gases impinge at every shot, driv- 
, ing the piston to the rear against a spiral spring. The latter, being 
then under compression, forces the piston forward again as soon 


CHAPTER XVIII. PLATE IV. 



HEAVY BROWNING MACHINE GUN, WATER-COOLED, ON 

TRIPOD MOUNT. 



622 


Naval Ordnance 


as the powder pressure has been relieved; and from the motion 
of the piston back and forth in the gas chamber the required 
operation of the mechanism is obtained. 

822 . Plate IV shows the “ heavy Browning machine gun, zvater- 
cooled,” mounted on a tripod mount. It is so designated to 
distinguish it from the “ light Browning which is designed to 
fire from the shoulder, and from the ,f air-cooled Browning ” used 
in airplanes. This gun is of the type that utilizes the recoil to 
operate the automatic mechanism. As viewed from the outside, 
it consists of a gun frame enclosing the working parts, a barrel, 
surrounded by a water jacket for cooling purposes, a front and a 
rear sight, the latter being of the sliding-leaf type, a grip, and a 
trigger. Extending through the gun, just in rear of the water 
jacket, can be seen the feed slot through which is fed the cartridge 
belt. At each shot the belt is advanced the width of one pocket, 
a cartridge is withdrawn from the belt by suitable mechanism, and 
is fed into the chamber of the gun to continue the firing. 

823 . The working parts of the gun consist of the bolt, the lock¬ 
ing mechanism, the tiring mechanism, and the driving mechanism. 
Of these, the bolt is the most important, as well as the most com¬ 
plex, part. It acts as a breech closure or “ fermeture ” during 
firing; it receives the recoiling force of the gun, and upon being 
released by the “ locking mechanism ” after firing, slides to the 
rear against a recoil bu ffer, at the same time compressing a counter¬ 
recoil spring that drives it forward again to close the breech; it 
provides means for feeding the cartridge belt forward after each 
shot; it carries an extractor that withdraws a live cartridge from 
the belt and loads it into the chamber, and an ejector that throws 
the spent case clear of the gun. In addition, it carries a portion of 
the firing mechanism. 

Plate V shows the working parts of the Browning machine gun. 
In Fig. i the bolt (I) is shown in its forward or firing position, 
resting over the barrel extension (28) and closing the breech. 
In this position a breech lock extends upward from the barrel 
extension, engaging behind recoil shoulders in the under surface 
of the bolt, thereby locking the bolt to the barrel and barrel exten¬ 
sion during firing. The breech lock cannot be seen in the photo¬ 
graph, but the breech lock pin (31) secured to it is shown pro¬ 
truding from a slot in the side of the barrel extension. Just above 


CHAPTER XVIII. 


PLATE V. 



Fig. i. 



Fig. 2. 





Fig. 3- 

BREECH MECHANISM, BROWNING MACHINE GUN. 


i 

1. Bolt. 

2. Bolt Handle. 

9. Cocking Lever. 

10. Cocking Lever Pin. 

12. Driving Spring Rod. 

13. Extractor. 

14. Extractor Cam Plunger. 

16. Extractor Cam Plunger Pin. 

17. Ejector. 

18. Ejector Pin. 

25. Barrel. 

28. Barrel Extension. 


29. Barrel Locking Spring. 

31. Breech Lock Pin. 

40. Lock Frame (right hand). 

41. Lock Frame (left hand). 

43. Lock Frame Rivet. 

44. Lock Frame Guide Pin. 

45. Accelerator. 

46. Accelerator Pin. 

50. Barrel Plunger Guide Pin. 

51. Trigger. 

52. Trigger Pin. 

56. Lock Frame Spacer Rivet. 







624 


Naval Ordnance 


the barrel a cartridge is shown, held between the extractor and the 
ejector in the manner in which it is withdrawn from the belt. At 
the side of the bolt is the bolt handle (2) , used in drawing the bolt 
to the rear by hand for the first shot. 

Fig. 2 shows the parts of the gun in the recoiled position. The 
bolt is seen to be almost clear of the barrel extension, and resting 
on the lock frames (40 and 41). The extractor, in this position of 
the bolt, has been forced downward by a cam surface in the cover 
of the gun, so that the cartridge it carries is now properly pointed 
to slide into the chamber. A portion of the cartridge case can be 
seen in the groove in the top of the barrel extension. 

Attention is called to the difference in location of the barrel 
extension, with respect to the lock frame, in Figs. 1 and 2. In 
Fig. 1, which shows the firing position of the various parts, the 
barrel extension is separated from the lock frame a little more 
than half an inch, whereas in the recoiled position, shown in Fig. 2, 
the barrel extension and lock frame are in contact. The reason 
is this: the barrel and barrel extension recoil with the bolt a short 
distance after firing. As previously noted, the bolt is locked to 
the barrel extension at the instant of firing. Obviously it must 
remain locked for a fraction of a second thereafter, while the 
bullet travels down the bore; consequently provision is made for 
all three parts to recoil together. It will be seen in Fig. 1, however, 
that the breech lock pin (31) very shortly passes under the beveled 
end of the lock frame, which forces the pin down and causes the 
breech lock to disengage from the shoulders in the under side of 
the bolt. (In Fig. 2 it will be noted that this has happened.) The 
bolt then slides to the rear freely, receiving an added impulse in 
that direction from the accelerator (45) (shown in Fig. 3), which 
communicates to the bolt the residual recoiling energy contained 
in the barrel and barrel extension. 

Since the bolt recoils with considerable force, means must be 
provided to absorb the shock of impact as it is brought to rest in 
its extreme rearward position. The bolt strikes against a buffer 
plate at the forward end of the grip, from which the shock is 
transmitted to a cushion composed of fiber washers inside the grip, 
thus stopping the bolt without undue strain or jarring of the gun. 
As the bolt slides to the rear during recoil, it compresses a counter¬ 
recoil spring known as the driving spring, and in so doing stores 


Aircraft, Anti-Aircraft, Field Guns 625 

up energy sufficient to force it back to its firing position. As soon, 
therefore, as it conies to rest against the buffer, the driving spring- 
forces it forward again to the position shown in Fig. 1. At the 
same time, the barrel add barrel extension are driven forward to 
their firing position by the barrel plunger and plunger spring, 
located between the right and left lock frames. 

824 . Only a part of the firing mechanism of the gun is visible 
in the figures. The mechanism consists of a trigger (51), a cock¬ 
ing lever (9), a scar and scar spring, a firing pin and firing-pin 
spring. The function of the cocking lever is to draw the firing pin 
to the rear, at the same time compressing the firing-pin spring. In 
its retracted position the firing pin is held by the sear until the 
trigger is pressed, when it flies forward against the primer. This 
action is brought about as follows: The long arm of the cocking 
lever extends through a hole in the top plate of the gun frame. In 
the position shown in Fig. 1, the firing pin has been released and 
has struck the primer, thus firing the gun. The bolt recoils, carry¬ 
ing with it the cocking lever. In so doing, the long arm of this 
lever comes in contact with the after edge of the hole in the top 
plate, causing the lever to pivot about its fixed point to the posi¬ 
tion shown in Fig. 2. At the same time, the short arm of the 
lever is thrown in the opposite direction, drawing with it the 
firing pin. The latter is drawn back until its head rests in a notch 
in the sear, which locks it in that position until the sear is pulled 
downward by pressing the trigger. As the bolt slides forward 
after recoil, the long arm of the cocking lever strikes the forward 
edge of the hole in the top plate, causing it to pivot again to the 
position shown in Fig. 1, ready to repeat the operation of cocking 
the gun. If the trigger is pressed continuously the gun fires auto¬ 
matically each time the long arm of the cocking lever is thrown to 
the rear. 

825 . In a previous paragraph, the statement was made that the 
cartridge belt is fed through the feed slot by the action of the 
bolt. The actual mechanism involved in this operation consists 
of the belt feed slide which moves back and forth in its grooves 
in the cover of the slot, and the belt feed pazvl which is carried on 
the slide. The pawl acts as a ratchet, moving the belt forward 
one cartridge width with each complete cycle of operations of the 
gun. The reciprocating motion of the slide is obtained through 


626 


Naval Ordnance 


the belt feed lever, which is pivoted at its center in the cover of the 
gun frame, and has at one end a lug that follows the diagonal 
cam groove shown in the top surface of the bolt. As the bolt 
slides back and forth in an axial direction, the arms of the belt 
feed lever are forced to move back and forth in a transverse direc¬ 
tion, thus giving the desired motion to the belt feed slide. 

826. The water jacket surrounding the barrel of the gun is for 
the purpose of cooling the barrel, which would otherwise become 
very hot due to continuous firing. The jacket consists of a steel 
cylinder, threaded at each end, the forward end screwing on to the 
end cap and the after end to the trunnion block. The joints in 
each case are sweated together. A bearing, packed with asbestos 
to make it water-tight, is provided for the barrel in the end cap. 
A similar bearing for the barrel and barrel extension is located in 
the trunnion block. 

At the top of the water jacket, near its after end, is a filling hole. 
A drain hole is located in the bottom of the end cap. Each of 
these holes is closed by a screw plug, fitted with a chain fastening 
to prevent its being lost. 

A steam vent is provided in the end cap to allow for the escape 
of steam as the water becomes heated. This vent is connected with 
an inner steam tube within the water jacket, which tube has two 
holes in its upper surface, one near each end. An outer steam tube, 
somewhat shorter than the inner tube, slides over the latter, auto¬ 
matically covering whichever hole happens to be at the lower level. 
In this way, water is prevented from escaping, steam only being 
allowed to pass out of the vent in the end cap. 

827. Operation of the gun.—The following description is given 
of the action of the gun during a firing cycle: 

Backward motion. —With the gun loaded and in the ready-to-fire 
position, the trigger is pressed. The forward end of the trigger, 
being engaged with the sear, causes the sear to slide downward 
in its groove in the rear end of the bolt against the lifting action 
of the sear spring. This releases the firing pin from the sear 
notch, and the firing pin is driven forward by the force of its 
spring until it strikes the primer and fires the gun. 

The barrel, barrel extension, and bolt then recoil together. After 
traveling about half an inch they are unlocked, the rearward 
motion of the barrel and barrel extension is arrested, and the bolt 


Aircraft, Anti-Aircraft, Field Guns 627 

continues to the rear. During its travel, energy is stored up in the 
driving spring for the counter-recoil movement. 

The backward motion of the barrel and barrel extension after 
unlocking is gradually transferred to the bolt through the accel¬ 
erator, which functions as a steadily increasing lever bearing 
against the lowest portion of the rear of the bolt. The accelerator 
gains momentum as it swings rearward, and imparts an accelerated 
motion to the bolt, so that the latter will complete its backward 
motion against the action of the driving spring. The accelerator 
also holds the barrel and barrel extension in their rearward posi¬ 
tion until the bolt returns and forces the top edge of the accelerator 
forward, thus unlocking the barrel extension from the lock frame. 

At the beginning of the backward motion of the recoiling parts, 
the extractor starts a cartridge from the feed belt. When the bolt 
is unlocked from the barrel extension and starts to travel rearward, 
a “ T ’’-cut in the front part of the bolt draws the empty cartridge 
case from the chamber. As the end of the case clears the after 
end of the chamber, the shell falls out, or is forced out by the 
ejector. At the same time, the new cartridge is lowered to position. 

During the rearward movement the cocking lever, playing 
between the two shoulders in the top plate, cocks the firing pin 
against the action of the firing-pin spring. It is held cocked by the 
sear. 

From the beginning to the end of the backward motion the feed 
lever slowly moves the belt feed pawl to the left, so as to engage 
the next cartridge in the belt. 

The backward motion of the bolt is limited by the bolt striking 
the bufifer plate. 

Forzvard motion .—The bolt starts forward under the action of 
the driving spring. The feed lever moves another cartridge over 
into the feedway. The live cartridge, that was carried to the rear 
by the extractor during recoil, is placed in the chamber, and the 
extractor is raised into position to extract the new cartridge just 
put into the feed way. 

As the bolt nears the limit of its forward movement, the lower 
rear lugs again come in contact with the accelerator, swinging it 
forward on its pivot. This gradually slows up the forward motion 
of the bolt and, at the same time, releases the barrel and barrel 
extension, which then move to their forward position with the bolt. 


628. 


Naval Ordnance 


The barrel plunger spring comes into play at this point and assists 
the driving spring in picking up the added weight of the barrel 
and barrel extension. While going forward, the breech lock is 
raised by the sloping surface of the breech-lock cam until the lock 
engages behind the recoil shoulders on the bottom of the bolt. 
This action locks the breech. 

The sear, being attached to the bolt and moving with it, can 
engage with the trigger only when the parts are in their forward 
firing position; consequently the firing pin cannot be released 
before the breech is locked. If pressure on the trigger is main¬ 
tained continuously, the cam surfaces on its forward end engage 
with similar surfaces on the sear and release the firing pin at the 
proper time, so that the gun fires automatically until the trigger is 
released. 

3 -Inch Landing Guns. 

828 . Landing guns supplied to U. S. Naval vessels are all 
3-inch guns, 23 calibers in length, with a muzzle velocity of 1650 
foot-seconds. They are mounted on mobile carriages, each gun 
being provided with a limber for the transport of ammunition. 

Plate VI, Figs. 1 and 2, shows the 3-inch landing gun Mark IV, 
at present supplied to all battleships. The gun consists of a forged 
steel barrel, with two hydraulic recoil cylinders in one with it. 
The latter are located one on each side of the barrel, a little below 
the axis of the bore of the gun. 

The gun and recoil cylinders rest on (not in) the slide, the 
former being provided with two gibs which fit under the edges 
of the slide and hold the gun to it during recoil. The top plate of 
the slide is made to conform to the contour of the gun. and forms 
a smooth bearing surface for it during recoil and counter-recoil. 
The slide itself rests on, and is pivoted to, a turntable, which 
in turn pivots on the axle and is movable vertically. 

The trail is built up of steel plate and has bearings for the axle 
in its forward end. At its rear end is the spade, with the trail eye 
cast in it. A trail wheel, for use in transporting the piece, is 
removed in action, allowing the spade to be imbedded in the ground 
to prevent movement of the carriage to the rear on recoil. Secured 
to the side of the trail is the combination rammer and sponge, with 
the handle to be used with same. The trail handles and the loop 
for securing the drag-rope snap hook are riveted to the trail near 
its after end. 


Aircraft, Anti-Aircraft, Field Guns 629 

The carriage is provided with two wheels, to support the gun 
and to transport it from place to place. Two ammunition boxes, 
each containing 12 rounds, are carried on the carriage directly 
over the axle. Below them are the tool boxes. 

The elevating gear, consisting of the elevating wheel, the screw 
case, and the inner and outer screzvs, is shown in section in Fig. 4, 
Plate VI. By turning the elevating wheel, the shaft and the pinion 
secured to it are turned. This causes the screw case to revolve, 
which transmits motion to the outer screw and thence to the inner 
screw, raising or lowering it, depending on the direction in which 
the elevating wheel is turned. By so doing, the gun is depressed 
or elevated. 

A traversing gear, consisting of a traversing screw operated by 
two handwheels, provides a limited amount of lateral motion to the 
slide. A total train of io° can be obtained in this way. For 
greater angles of train, the spade must be lifted and the gun 
slewed around by means of the trail. 

829 . The recoil system consists of two hydraulic recoil cylin¬ 
ders, both of which are integral with the gun and recoil with it, 
and two pistons and piston rods, the latter being secured to the 
front enforcement at the forward end of the slide. Each cylinder 
is fitted with a filling plug and a drain plug. An equalizing pipe 
connecting the two cylinders insures an equal amount of liquid in 
each of them. 

Fig. 3, Plate VI, shows a longitudinal view of a recoil cylinder 
in section. It will be seen that the cylinder contains, in addition to 
the recoil piston and liquid, the counter-recoil springs as well. 
The latter consist of three sets of inner and outer springs, with 
spring separators between each set. 

The piston rod, it will be observed, is hollow bored for about 
half its length from the rear face of the piston. I his bore is 
known as the tlirottling-bar socket. 

The piston carries the throttling ring, screwed into its rear end. 
Forward of the throttling ring is a recess called the piston throttling 
chamber, which is connected by means of port holes to the piston 
annular groove. The piston is allowed a .005-inch clearance in the 
cylinder, and has a shallow annular groove around it to give the 
effect of liquid packing during recoil. At its forward end is the 
spring collar, against which the springs bear. This collar is slightly 


630 


Naval Ordnance 


smaller in diameter than the bore of the cylinder, to allow free 
passage of recoil liquid from the cylinder to the piston annular 
groove and thence through the port holes to the throttling chamber. 

Extending into the throttling-bar socket in the piston rod is 
the throttling bar. The latter bears on its after end the throttling- 
bar nut, which screws into the rear end of the recoil cylinder. The 
throttling bar is slightly shorter in length than its socket. It tapers 
gradually for the greater part of its length, then jumps to a slightly 
larger diameter in a quick slope, and is cylindrical for the re¬ 
mainder of its length. The throttling bar passes through the coned 
throttling hole in the throttling ring, then through the throttling 
chamber, and slides in the throttling socket. There are 90 throt¬ 
tling-bar socket escape holes drilled through the piston rod. These 
holes allow the free passage of liquid to and from the socket, and 
serve also to check the counter-recoil. At full counter-recoil, the 
forward end of the throttling bar is about .2 inch forward of the 
last escape hole, and the rest of the socket serves as a dash pot. 

Checking of the recoil is accomplished by forcing the liquid 
from the cylinder through the piston port holes into the throttling 
chamber, and then through the tapered hole of the throttling ring, 
around the throttling bar. The clearance at this point is large at 
first, and allows an easy recoil. The tapered throttling bar, how¬ 
ever, gradually closes the hole in the throttling ring, and, with 
the help of the springs, checks the recoil. The springs then return 
the gun to battery. 

A special packing is provided at the front cylinder head to 
prevent the escape of liquid around the piston rod. There is 
first the annular V packing, backed by a packing ring sliding in 
the bore of the cylinder head. This is followed by a ring of hemp 
packing, which is pressed in place by the cylinder-head gland. 
Four holes in the cylinder head admit liquid to the V packing. 
The pressure of this liquid serves to set the packing against the 
piston rod during recoil and prevents leakage of the recoil liquid. 

830 . The sight provided with this gun consists of a peep sight, 
with ordinary cross-wires in the front sight. There is also an 
auxiliary finding sight, consisting of a notch on top of the peep 
sight and a point on top of the front sight. 

Plate VII shows a later type of 3-inch landing gun. It is pro¬ 
vided with a shield, and has a split trail to allow for high angle of 


OLP ft 


CHAPTER XVIII. PLATE VI. 



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3-INCH LANDING GUN MARK IV, WITH CARRIAGE. 














































































































































































































































































































CHAPTER XVIII. PLATE VII 




Fig. i.—3-Inch 23-Caliber High-Angle Landing Gun. 


Fig. 2.— 3-Inch 23-Caliber High-Angle Landing Gun. 



















Aircraft, Anti-Aircraft, Field Guns 


631 


elevation. It is fitted with a panoramic sight to be used for indirect 
fire. This sight is a vertical telescope so fitted with reflecting 
prisms that the pointer, with his eye at the eye-piece, which is fixed 
in a horizontal position, may bring into the field of view an object 
situated at any point in a plane perpendicular to the axis of the 
telescope. 

Below the gun is located the recoil cylinder. For o° elevation 
the normal recoil of the gun is 42 inches. At high angles of ele¬ 
vation, however, this recoil must be shortened to prevent the breech 
of the gun from striking the ground. This is accomplished by 
decreasing, at high angles of elevation, the available port area 
through which the recoil liquid can escape during recoil. A special 
gear is provided that automatically blanks off a certain number of 
escape ports as the gun is elevated. The result is that the gun 
is checked with greater force, and comes to rest in a shorter space. 

Above the gun is the recuperator which returns the gun to 
battery. No counter-recoil springs are provided at all. The 
recuperator, to all intents anff purposes, is an air compressor. As 
the gun recoils, the air on one side of the piston becomes highly 
compressed, with the result that as soon as the rearward motion is 
stopped, the air pressure forces the gun back to battery. 













































































































































